(lead dev here). Not intended, as I don't use Rails myself. But I would of course support every PR making Bmg compatible/great with it.

If you use Sequel, it should work fine

https://github.com/enspirit/bmg#connecting-to-a-sql-database

Just like any gem. You can create models without inheriting from ActiveRecord.

Intended - I have no idea.

Possible - Absolutely.