What interests me personally, also in light of this snarky comment here http://news.ycombinator.com/item?id=1924487 is whether Ruby 2.0 will do away with reopening classes and only allow the much better Refinements.
This will break most of the code out there, but in light of doing it cleanly, it would probably need to be done. On the other hand, a change like that will make sure that we might never see significant adoption of Ruby 2