Really interesting. I like the way that the total ordering approach makes it clear when an earlier compatibility-version (e.g. 1._) is being maintained alongside a later version (e.g. 2._). That's something that isn't expressible in SemVer.
Do you mean instance where the release number be the same, as in 1.77 vs. 2.77? Because that likely won't happen, as due to the different compatibility these should be different releases. Or do you mean, if the release numbers are reasonably close, as in 1.77 vs. 2.78, and then maybe 1.79 again?