Here's an incomplete (though essentially test-passing) patch that flips more of imp into importlib.  It builds on Brett's patch.  The gist is that imp.py is a minimal wrapper around importlib, which uses _imp directly.

Ultimately the things implemented in Lib/importlib/_bootstrap.py should be yanked out of Python/import.c (and Python/dynload_*.c).  I expect that this will wait for the bootstrap merge (#2377) to land.