I'm working on a temporal document store in my spare time. If done right and you have an index structure which let's say indexes each revision of a table (in my case binary XML or JSON as of now) as in Git for instance you simply append a new RevisionRootPage. This page is indexed of course and points to the former revision-data. Should be super fast, so you don't have to replay changes made in the meantime. Even if I'd write to a distributed log for instance and would read from it the changes since revision n. I think that way you can also version the whole database easily.

https://sirix.io / https://github.com/sirixdb/sirix