What about adding user entries to the "switchserver table"?
Currently, if you want to access an arbitrary wiki table, you need to
look it up first in toolserver.wiki. Seems appropiate to extend that to
user databases. Frameworks setting db connections would need little
changes to also handle user dbs like they do with wmf views. (I'd
actually put it into a new table eg. toolserver.databases, but changing
the db name used in the framework at the same time -keeping wiki for
other uses, of course- should be trivial)
Regards