(merging from other meta thread I made about this)
My area is not physics. However, this was the best thing that Stack Exchange had to offer me, and I decided I really liked it, so I've been active here for a number of months (I mostly used the username zassounotsukushi). Lately I started to think it might be worthwhile to make an Area 51 attempt for Nuclear Engineering, which is what I do.
http://area51.stackexchange.com/proposals/38647/nuclear-engineering
We already have a tag for it! At 25 questions it's not much, but most nuclear questions are blatantly not relevant to Physics SE anyway, so I figure, who knows what you would get if you invited questions about it?
https://physics.stackexchange.com/questions/tagged/nuclear-engineering
I haven't yet, but I recognize that in order for the proposal to succeed I would need to plaster it around nuclear related listserves, message boards, maybe use fliers, and get other people to help it go viral as well.
You could make arguments for why this may or may not work, but I could see it working. The Electrical Engineering SE comes to mind, which is funny because I never found that to be very useful, just because the knowledge is so incredibly specific to the application and broad as well. Nuclear is much more narrow, but if you allow fairly practical and specific (to regulations, designs, etc) then there's certainly no end to the obscurity of questions you could encounter.
Either way, I would love to see lots of people from this site share what they think at the proposal. I'm wondering if 200 people is more than we could hope to recruit, or if we could ever have a high enough volume of questions. But the entire point of stack exchange kind of feels like controlled anarchy anyway, so might as well start it out and see what happens, right?