The following animated gif pretty much sums up the basic idea:
I figure this will just keep going and going. Russia and China may bow out, but the economic benefits accruing to membership in the EU will probably prove too positive for others to resist. The EU will also probably continue to gel as an administrative union, given the observation that once a group starts making laws, it generally doesn't stop.
Despite the possible downsides ( abusable hegemony ), the EU's continued expansion provides me with one of the few glimmers of hope for a workable coordinated future.