The difficulty now is that you'll have to compete against Stack Overflow, whereas Stack Overflow had to compete with the paywalled Experts Exchange. Both for-profit and non-profit will have a very hard time unless Stack Overflow really goes off the rails in Quora-style it will probably stick around.

Also I think people underestimate how much effort goes in to moderating Stack Overflow, and how delicate the entire system is. There's already a whole bunch of Open Source Q&A software out there and I'm sure one of them will work fine, that's not really the hard part, and managing servers is also "just" a matter of spending time. Moderating and managing it all is much harder and more time-consuming; there are people whose ability to hold down a job or finish their homework quite literally depends on being to ask questions on Stack Overflow: there's a lot of incentive to abuse the crap out of it, more so than many other sites.