I'm interested in it as a library or an open source tool that I can integrate, but as a paid product, I believe it falls a little bit short of an MVP.

What's unique about what you have here is the realtime collaborative editing. We use NestaCMS (which also understands Markdown) hooked up to a Dropbox folder in a few places. The functionality is similar, but there's no in-page editor, and we can't collaborate in real time.

Both of those things have value to me, but I have serious reservations about jumping on to a wiki product that I can't control. Documentation is a complete pain in the ass. When I put time in to it, I need to feel 100% confident that I won't have to abandon it at a future date; either because I run up against a feature ceiling, or because you disappear. And if I do have to leave, I need to be able to get my information out of the system.

That's tough to answer (pricing is tough!). As a single consumer, not much (e.g. under $20/month). As a business, potentially a lot more. If you're actually marketing it to enterprise or at least company teams, they're budget (and features they'd require) are different.