I'm in this situation right now. How would one go about solving this?

To keep this simple, I'm thinking exporting just the necessary data from each db and inserting that to a stats db (having a source column to each table, referring to the original db). Then load the stats db with Metabase or something.

Migrations on the stats db may be a bit of a pain, as well as making sure that all data is exported and imported correctly every time.

I'm sure there are better ideas.