I don't have any hard evidence, but I suspect that the people who have already jumped ship from GH only did so with solo projects or with very small teams. The switching cost for those people/teams is always going to be pretty low.
Looks like a good project. You should probably mention very, very early on in your docs, though, that this is for Bitbucket Server (self-hosted) and not for Bitbucket Cloud (bitbucket.org).