Dataflow and PowerBI Gateway - Sourcing data dynamically

I was re-reading your original post and something occurred to me... have you tried to maintain a table with meta data, that is, a table that will keep track of all the DB servers and DB names as they come and go?  This would allow you to create a query that connects to the DB containing this meta data table, and using that table, you can in M select any or all of your databases and thus ingest their data.