Hmm. It's a good idea, but typically rollbacks/downgrades are ONLY recommended (by Plex Inc.) when using a beta and downgrading back to stable. For large updates, like from 1.5.x to 1.6.x, etc., this would not work. With big point releases, most of the time large DB changes come along, thus making a downgrade impossible.
We can look into this perhaps, but I don't think Plex supports it so much.