This is another one of the three reasons I still have for exiting the app to the mobile site, but it's a tricky one to implement. I've made a pretty ambitious first stab at a mockup:
Access through the EllipsiSideways.
New window slides open, with list of revisions. Actual implementation maybe shouldn't attribute everything to me. Open to debate though.
Tapping one brings up that particular revision:
It's a lot of work, and a lot of new pages. Working through this, I can understand why this hasn't been done yet. Hopefully this workflow is a good start for the conversation though, as it's a valuable tool to have.