From what I understand of VersionPress, it's more focused on version controlling a single instance of a website. As far as I understand, it doesn't achieve two of the main things I'm excited about Mergebot because of:

- to provide teams working on a single website with a way of merging databases when they've been working on two seperate instances of the same site during development on a platform like Vagrant (as commonly happens in larger agencies).
- to provide a way to merge a development database into a live database without having to redo all the posting of content, updating of options etc as you currently have to do.

While what VersionPress does is valuable, what Mergebot will bring - if the guys are successful - is nothing short of game changing when it comes to the development of larger sites.

I'm happy to be corrected if I'm wrong though. :)