Congratulations! Vagrant is awesome. The blog post says that future releases in the 1.x series will not necessarily be backwards compatible. Does this mean you are not adhering to SemVer? If so, why not?
I always say this warning to disclaim myself from future backwards incompatibilities, but if I follow 1.x like 0.x at all, then they'll be minimal.
Vagrant 2.0, of course, will introduce long term stability, like Vagrant 1.0. But that is far off. :)