The image and oldimage tables RfC proposes to change the database layout from having two tables for "current" and "old" image (file) records, to having one for the file, and one for file revisions.
The most recent version of each image is stored in the image table, with historic versions stored in the oldimage table. This structure resembles cur and old, with all the nastiness that comes with it. In MW 1.5 we ditched cur/old in favor of page/revision, but we never did a similar thing for files.
We talked about this a bit at the 2011 Amsterdam Hackathon and decided that, while it's complex and hairy, we want to do it at some point in the future.