I had a side project which was basically this (at least this was my [company] for [x] summary of the project) a couple of years ago. I always wondered why StackOverflow weren't doing it, and after years of wondering this I just built it myself.
I tried to publicise it a bit (not a lot, in fairness) and didn't generate much buzz. I even speculatively applied to YC with it, with the beta written and running, and got no call for an interview even. After that I lost enthusiasm for the idea, and moved on to other things. Seeing this has reminded me of it.
What do people think of this? Useful product? Would you pay for it?