I am observing with great interest the development at Area51 for new Question/Answers sites to be opened with the StackExchange system. One thing that makes me cringe a bit is the very strong fragmentation. I think this stems either from the need of personal protagonism of each person (nothing bad with it, progress happens also thanks to personal protagonism), or by lack of notice that a similar proposal has already been done. I could be wrong though, and I accept criticism on this point.
The main problem, however, remains. Opening a StackExchange site is damn hard. First you have to find at least 60 people interested in the site. Then, when this limit is reached, a large amount of people (in the hundreds, but it really depends on the reputation of each participant) must commit and promise to create momentum for the site, adding questions and answers. When this amount is reached, the site is open and stays in closed beta for seven days. During this time, the committers have to enrich the site so that the public beta (which starts after the first seven days) gets enough hits and participants to show a self-sustained community.
That said, I checked the situation. Many sites are already open, but there is a critical lack of fundamental and potentially "large-community" sites, such as Music, TV, Health, Travel. The system at Area51 is engineered to let unpopular proposals die out, while other, more popular ones gain traction, but in some cases, some coalescence would greatly help to reach the threshold (assuming disjoint followers, of course), at the price of losing specificity, and would allow smaller communities to get their space. For example, Guitars is likely to open, Drumming is less likely as there are less drum players. Having a more general topic would allow both communities to thrive on a very powerful, but more general musical performance site. Please note that generalization should not be a big issue, as StackExchance sites allow questions to be tagged with labels, and the users can choose which labels to follow and which ones are not of their interest.
On the other hand, people will most likely subscribe to something they are (e.g. I am a guitarist, so let's search for a "Guitars" proposal, instead of searching for a "Musician"). These two opposite forces end up creating a potential impasse. I think a coordination effort is missing to coalesce fragmented sites. While I am not trying to be such a coordinator, I am providing some food for thoughts.
This is a live post. I will update it as much as my spare time allows doing it, and it will never be up-to-date. I am just throwing a line of reasoning on the current situation for interested readers, in particular from Area51. I accept ideas and criticism in the comment section.
Music Audio Recording and Production (63 commit), Guitars (57 follow), Musical practice and Performance (35 followers), Music Education (11 follow), Drumming (10 follow), Musicians (10 follow), Music Theory (5 follow), Music History (5 follow), Jazz theory (2 follow), Classical guitar (2 follow), Musicians' gear (1 follow), Electronic Music DJs (5 follow), MusiciansKnow (2 follow)
Science Statistical Analysis (beta), Mathematics (beta), Theoretical Computer Science (347 commit), Physics (87 commit), Astronomy (48 commit), Cognitive Science (32 follow), High Energy Physics (31 follow), Bioinformatics (18 follow), Biological evolution (12 follow), Meteorology (9 follow), Biology (9 follow), Mass Spectrometry and Proteomics (9 follow), Chemistry (6 follow), Space Exploration (5 follow), Entomology (2 follow), Particle Physics (1 follow), Scientific techniques (1 follow), Robotics (1 follow), Computational Fluid Dynamics (CFD) (5 follow), Numerical Analysis (3 follow), How Stuff Works?, Amateur Rockets and Rocketry, Energy efficiency in buildings and organizations
Teaching and education Popular Natural Science (28 follow), Science@Home (7 follow), Astronomy education in schools (12 follow), Physics Education (4 follow), Computer Science Education (4 follow), Kx12 (3 follow), Homework Help (3 follow), Software students (2 follow), Children’s Sport Coaching (2 follow), EFL/ESL Teachers (1 follow), Games for education (13 follow), MathUnderflow (2 follow), IT literacy Education (2 follow)
Books Science Fiction (39 commit), Star Trek (40 follow), Books (27 follow), Middle Earth (24 follow), Star Wars (18 follow), Ook! (16 follow), Comic books (10 follow), Literature (2 follow), Murder Mystery Suspense (1 follow)
Writing Writing (43 commit), User Assistance/Technical Communication (23 follow), Technical Writing (16 follow), Science writing (11 follow), Science Fiction Writing (9 follow), Blogging and Copywriting (4 follow), Copywriting & applications (3 follow), After Writing: Getting it Published (2 follow), Blogging and the Blogosphere
Religion (or lack of) Biblical Hermeneutics (63 follow), Christian Worship Leading and Service Design (43 follow), Atheism (40 follow), Hare Krishna (23 follow),`Christianity <http://area51.stackexchange.com/proposals/11655/christianity>`_ (11 follow), Textual Criticism of the Bible (9 follow), Torah (8 follow), LDS (Mormon) Q&A (8 follow), Jewish Services, Tradition, and Halakha (7 follow), Jewish Law (6 follow), Lumdus (4 follow), The Bible Code (3 follow), God - Let’s Discuss! (1 follow), Spiritual Enlightenment (1 follow), Islam, Spiritual Warfare Defense
DIY and crafting Home Improvement (private beta), Woodworking and Carpentry (35 follow), Metalworking and machining (10 follow), Do it Yourself (6 follow), Spare Parts (5 follow), Breakdown Voltage, Cars Problems
Physical activity Exercise and Fitness (40 follow), Running (33 follow), Hiking (22 follow), Yoga (22 follow), Martial Arts (21 follow), Backpacking, Hiking and Camping (19 follow), Snowboard and Ski (10 follow), The Great Outdoors, Camping, Survivalism (9 follow), Extreme Sports (7 follow), Rowing (6 follow), Technical Climbing (and any other technical sport like caving, sky / scuba diving, etc.) (5 follow), Archery (4 follow), Mountaineering and Climbing (including Indoor Climbing) (3 follow), Diving (3 follow), Brazilian Jiu-Jitsu (2 follow), Skydiving (2 follow), Barefoot Running (2 follow), Mountainbiking (2 follow), Tennis (2 follow), Children’s Sport Coaching (2 follow),`Sports Coaching <http://area51.stackexchange.com/proposals/7179/sports-coaching>`_ (3 follow), Triathlon (9 follow), Sport Rules (8 follow), Golf, Body Building, Ultimate Frisbee
Languages: English Language & Usage (141 commit), Japanese (30 follow), English/French Translation (25 follow), Linguistics (21 follow), Chinese language (18 follow), Translation (10 follow), Language learning and language hacking (9 follow), Esperanto (7 follow), Planned Languages (5 follow), Translators and Language Professionals (5 follow), French-English Exchange (4 follow), Non-English Language Learning (3 follow), Indian English (2 follow), Irish (1 follow), Proofreading (1 follow), Classical Chinese (1 follow), EFL/ESL Teachers (1 follow), Indic Q&A (22 follow),`Turkish Language <http://area51.stackexchange.com/proposals/3296/turkish-language>`_ (5 follow), English-Russian Exchange (34 follow), Spanish Language and Usage (1 follow), Italian Language and Usage, English / German translation, Spanish Translators / Traductores de español
Life abroad and traveling Travel (24 follow), Gaijin-san (16 follow), Immigration (16 follow), New York City (13 follow), Iceland (11 follow), London (6 follow), Texas (5 follow), Overland Travel (5 follow), Cozumel, Mexico (4 follow), Road Warriors, Frequent Flyers, etc. (for business travelers, mileage maniacs, etc.) (4 follow), San Francisco (3 follow), Vacations (3 follow), Italy (3 follow), Bangalore (2 follow), Cambridge - UK (2 follow), City Sights (2 follow), Portuguese Leisure (1 follow), Maine (1 follow), Argentina (1 follow), India (4 follow), México (3 follow), Sweden
Medicine and health Everything You Always Wanted to Know about Sex but were Afraid to Ask (11 commit), Weight Loss (13 follow), Medicine (11 follow), Diabetes (6 follow), Health (5 follow), Sleeping (3 follow), Drugs (3 follow), Sleep Apnea (2 follow), Endometriosis (1 follow), Weight Gain (1 follow), Food Safety (1 follow), Radiation Oncology and more (1 follow), Psychology and Psychiatry (0 follow), United States Medicare (0 follow), Metastatic Breast Cancer (1 follow), Sex & Sexuality (2 follow)
Pets and animals: Pets (11 follow), Beekeeping (9 follow), Animal Health and Behavior (9 follow), Equestrian (5 follow), Animal Hobbies (4 follow), Aquarium Hobbyist (14 follow), Saltwater Aquariums (12 follow)
History: History (32 follow), Mythology (17 follow), Greek Mythology (12 follow),`United States History <http://area51.stackexchange.com/proposals/1717/united-states-history>`_ (12 follow), Military History (9 follow), History of Computers and Computing (8 follow), Music History (4 follow), Historical Reenactment and Play (2 follow), The United States Civil War (2 follow)
There are some mixed points I would like to clarify and discuss. First, my classification is rather broad and, in some cases, far fetched. For example, poker players would cringe seeing Magic under card games, but really, Magic is a card game. Other cases could even be worse, but I tried to keep a very broad stance. The classification name (in bold) is not an index for a "generic community that should be opened in my opinion". It is just a guide.
Also, there is the problem of scientific Q/A that are very specialized. Some of them gain enough traction (maths and statistics). Others fall behind, I assume either due to a poorly collaborative community, insufficient Public Relations effort, or excessive specialization (which reduces the community to a handful).
In some cases, the communities focus on topics that tend to promote opinion answers, rather than factual answers. The most striking example are clearly religious Q/A sites. While some things can produce factual answers (for example: "in which parts of the bible X is discussed?" or "does the Buddhist discipline consider proper to eat meat?"), other questions are total opinions ("Does God exist?", or "Gay marriage law passed in X, how can we oppose it?" the most probable ones). Although such questions would be considered off-topic, or subjective and argumentative, religious sites are difficult to handle, unless they are handled like a philosophy Q/A site: who said this, where and when. Similar point with any political-oriented Q/A.
On regard of difficult to handle Q/A sites, there is "Everything You Always Wanted to Know about Sex but were Afraid to Ask". The site is definitely interesting from the medical point of view, but it must be kept with strong discipline, or it can diverge from its original intent pretty quickly.
Feel free to leave comments.