I don't count "unable to push" as a "natural upgrade", maybe it is a conceptual extension
though. git-svn let me push code to SVN 9 months ago, but that reeks like the start of a
flame war, so let's not, ok? :) Git clearly is NOT ... neither upgrade nor extension ...
anything like SVN, by clear (Linus') intent. (Food for another flame war, oh well.)