Very cool! I'm still looking around for a Sonos alternative. The biggest stumbling block for me is always finding something that can cooperate with my 3rd party podcast client on Android. I haven't seen any multi-room solutions that can do that at all, let alone satisfy all the other features I'm looking for.
No idea if it'll do everything you want, but
CasaTunes is a very nice alternative to Sonos. It also has iOS and Android apps. And I'm not sure for Android, but their site
mentions "CasaTunes Air: Play any iOS music App in any room in your home". If this is true for iOS, I don't see why this wouldn't work with Android. It might be worth checking out.