For the most part, anyone who did move to bbPress wouldn’t be on this forum, now would they? 
We don’t know. We only know Discourse. You could look at the BBpress world and see how people move to bbpress from other forums. You’d start here: Import Forums · bbPress Codex and then use one of those importers to figure out how to write one for Discourse.
It’s probably pretty hard, since I bet bbpress doesn’t know how to read a postgres database, but that’s probably solvable. Though I might do it for less once I looked at what was involved, I likely wouldn’t consider such a job unless the budget was in the $5000 range. It would take me a bunch of time to figure out a bunch of stuff about bbPress that I don’t want to know.
Solving that problem is what people here could help with.