Regarding the ABCs, I'm okay with it as long as invalidate_caches() is meant to be a part of meta path finders.  I had considered this while writing the patch, so how I had it wasn't a fluke.  The fluke was that I didn't bring it up for discussion like I had meant to do.

 Anyway, my rationale was that importlib.invalidate_caches() is specific to path entry finders.  My patch reflected this.  If invalidates_caches() were meaningful for meta path finders then we could address that later without losing backward compatibility.

As to pulling find_module() off Finder, I felt that having a distinct signature, while semantically unimportant, made a clearer distinction between the old and the new.