I would love having the ability to see the history of revisions and access the historical versions.

It would be a huge change to have it work the way that Workflow does, where you publish it, and the in-progress items can be switched to the new version or left on the version they were on, and historical logs can tell which version it was on.  Forms just isn't built to work in that way.  Just thinking how Forms has things set-up in the database and how it handles changes - I don't see that being possible without some really big changes to the structure of the system.

But maybe something in the middle...  Maybe every night, it identifies any processes that were changed that day, and saves an export of the process to the database - so we wouldn't have revision history for each individual change, but at least a snapshot of what it looked like at the end of any day that changes were made.  The individual instances would still work like they do now, entirely on the newest revision.  But the history of revisions (at least much of it) would be archived and could be retrieved if needed.  I would like something like that.

EDIT TO ADD: I currently manage changes with a Production environment and a Test environment.  When I need to make changes, I copy the process from Production to Test, make the changes I need, and then coordinate with the team members that wanted the change to review and try the process in Test.  Once they approve the change, I copy back from Test to Production, and that this point, any in-progress instances are updated.  There are one or two processes where I can't really have any in-progress ones (where version of the document is very important) - luckily those are not really active processes, so there is usually only a couple active that I can pester people to complete, or none active at all.  Most processes we accept it as a given that changes will be applied to items in progress.