One more side to this which is relevant to other discussions.
If I am rewinding back to before when a table was created, the current algorithm as well as any proposed algorithms will delete the reference to the relfilenode in the catalogs but not the file itself. I don't see how an undo subsystem would fix this.
Is this a reason to rethink the idea that maybe a pg_fsck utility might be useful that could be run immediately after a rewind?
