Currently: A query can only reference one database. ex: If i want to send to subscribers in our main database, but also import a custom list of a few people, I have to do this all as separate databases & query.

Proposing: It would be more efficient if I could build one query that pulls from the main database and then also pulls in other databases (like the custom list upload). And then the mailing can just go out once, to the one query.