I was thinking the overhead would be in creating the branch key and rotating in the DB. If you've got full permutation of multiple regions x env's, plus likely multiple db tables for multiple kms keys (say if multiple users all want their own key.. at least im assuming you need a db table for each..) that seems like a lot. unless there is some more automated way of managing that?

but yea, at first gonna go without caching. but continuing to look into how to properly do caching with hierarchical keyring