I would say that Yahoo Answers, answers.com, allexperts.com, wikianswer, askville, answerbag, yedda, and the hundreds of other generic "answer" sites have proven that this is a bad idea.
There is still a difference and that difference might be the key. Also, if you take all SO sites together, you still have the very wide common topic "technical".
If the topic becomes even wider, some clever tag-filtering/handling may be needed so a user could view the questions like they have been before. Also the reputation could be tagged base.
In any case, just because not-so-well-made and not so technical-centered sites with not anywhere near the features of SO have failed is not a proof that a general answer site is a bad idea.
Why? Those sites have done pretty well. I think it's a good idea. I really am annoyed by the variety of SO sites and the juggling you get when you encounter something that requires an overlapping of disciplines. It's pretty common for sysadmins to need to do a bit of programming and programmers to do a bit (or more) of sysadminning, and the questions aren't always immediately separated.
It should all be consolidated into SO and SO should be given "super-tags" or "categories" for server admin, programming, etc., and then you don't need a bunch of different sites/designs with fewer users. In short, take the reddit approach; allow users to subscribe to categorized channels that interest them and compile the front page based on that.
