If I worked for a big company, I'd love this (or, a Quora for a loose social network like HN people, YC companies, attendees of a series of security conferences, a university department, etc.). Makes a lot less sense for a 3 person startup (at that scale, email and/or wiki makes more sense).

I think Opzi was also potentially this at one point in the past, but just like everyone else doing "enterprise Q&A", pivoted away. I think there's no way to build something which makes money, is simple, is usable and worth using, and complies with stupid enterprise policies on Q&A.