We think that 2.2.0 works with it mostly correctly but we are finding some "gotchas".  Notably it looks like Google is sending some ACK messages after we register that the library is ignoring.

We will need to support InstanceID (tl;dr; Google is enhancing registraiton_id).  Passos and I are still digesting the volumes of stuff being rolled out from IO so we can't really give too many details right now because we simply don't know them (And Google is still updating their docs, fixing links, etc).

So the question to the list is :

 Do we delay 2.2.0 and include support for InstanceID and any other best practices Google has introduced or do we release 2.2.0, document / work around any gotchas and then prioritize GCM 3.0 support for 2.3.0?