Yeah yeah absolutely nothing. Just like any other feature committed to Postgres so far ;-)
I need to polish the chain conversion patch a bit and also add missing support for redo, hash indexes etc. Support for hash indexes will need overloading of ip_posid bits in the index tuple (since there are no free bits left in hash tuples). I plan to work on that next and submit a fully functional patch, hopefully before the commit-fest starts.
(I have mentioned the idea of overloading ip_posid bits a few times now and haven't heard any objection so far. Well, that could either mean that nobody has read those emails seriously or there is general acceptance to that idea.. I am assuming latter :-))