A potential problem that's nagging at me is that since everyone expects a string in __version__, nobody (except us) will look at the Version object for more information. Humans and presumably existing tools that look at __version__ will expect a string, so they won't think (or be able) to look for more info. They'll only see e.g. '1.1', whether they actually have the official 1.1 release or any other pre-1.2 version. Humans may get confused, simulation-running tools may store the wrong version (at least my stupid one would!), python packaging tools may fail to realize one package is different from another, and so on. Should __str__ be altered? 

(And if so, should it be altered to comply with http://legacy.python.org/dev/peps/pep-0386/? I think that's too much effort, and our existing Versioneer-supplied version is not compliant anyway, so at most I would add a feature request after merging this PR.)