I had plans to make a Python migration scripts from X to Flarum too, built with my pyFlarum package once I add database support to it (currently, it only allows you to login as user and perform tasks via the API). The database branch was started, and currently works to some extent, but it was never finished.
Unfortunately, I don't have enough motivation to prioritize this over my current couple of projects (and also due to lack of database samples to work with from different platforms), so it will have to wait.