So good news,

Topic support for GCM is trivial to implement.  In fact after 20 minutes I have most of the work done in the Android library.  The behavior of topics matches the behavior of categories.  I would like to propose some enhancements.

1) Changing categories/topics currently requires the application to unregister and reregister on UPS.  I would like to add a subscribe and unsubscibe method to the pushRegistrar interface which will subscribe and unsubscribe the device from topics.

2) All Message listeners receive messages from all topics the device is subscribed to.  I would like to extend registrar manager to be able to attach messages handlers per topic as well as globally.

This are both simple, easy changes which shouldn't be a lot of work and will really improve the push experience in Agdroid 3.0.