I'm pretty much looking for the same thing. It's sad how most of these project try to add their own layer ("vocabulary") on top of the relational semantics without first trying to surface as much of it as possible.

What I'd like to see is something that can connect to a pg server (or sqlite, or mariadb, but I think settling on one is more feasible) and tries to surface as much as possible of the underlying data representation, and add features that are translatable to how pg works, instead of just using pg (and in grist's case, sqlite) as a dumb backend.