IIUC, you're looking for candidates for semantic faces. In that case, I imagine that it would be helpful to gather a dozen or so popular themes, strip them down to the face-setting code, condense the specific settings down into categories, and then synthesize the lists into solid candidates.
This seems like the sort of effort that could be distributed. I would be willing to help out, but I don't personally use any of the more complex completion frameworks, so I might have a big blind spot for the search.
Let me know,