I'd like to see MAJOR.MINOR bundle versions.
Say you had developed a bundle and rolled it out to a bunch of machines, but then discovered that you needed to tweak the bundles install actions to improve it for ongoing installations but DON'T WANT IT TO REINSTALL on all the machines it has already been installed on - you make this a MINOR version change.
But if you DID want it to reinstall on previously installed machines, then you make it a MAJOR version change.