I've commented about this same issue recently, and it's very high on my wish list as well. It's becoming even more important as our team of Opto programmers grows.
I'll tell you what I'm doing now, because it may be helpful. Every time I want to track changes, I run three commands from the File menu: Print All Chart Instructions, Print Database, and Print Cross Reference. Save all three as text files. Put those three files into a Git repository, and you have some amount of change tracking.
For an added level, I actually have a custom script that splits the all chart instructions file into individual chart files. That way when I make a change, Git can tell me exactly which charts were changed. I do this because I have some strategies that have a few hundred charts and it's nice to see the individual chart changes.
Let me know if something isn't clear or if you have any questions about how I'm doing this. It's not a perfect option, but it's the best thing I can think of for now. Unlike some other types of projects, obviously this doesn't give you any real ability to revert to a prior version, but it does give you historical change tracking (and theoretically a "backup" of your code if you publish somewhere like Github, which is what I do.