Github is not something that should be replaced. Rather, a different kind of model needs to exist. Before Git, there were things like Subversion, for instance. All of that slowed way down after Git showed up to the party because people liked the fact Git was "easier to use" and eventually networking effects. When Microsoft purchased Git, the death knell had all ready sounded, but nobody was listening.
Did you confuse github with git? Indeed centralized git in Github is hardly any different from svn.