Spotify has been promising for months now to release "Spotify Connect" as a part of libspotify. Instead, they are steadily striking "exclusive deals" with one manufacturer after another (called "Spotify Partners") but knowingly ignore "Spotify Customers" like me, with slightly older hardware, but who might have been more loyal to Spotify then any new hardware buyers, loyal customers who are now desperately locked waiting for improbable firmware updates..
Onkyo also promised to add Spotify Connect to it's receivers line (specifically they mentioned NR-636 model). I have a sour feeling that my NR-626 model, bought just in October 2013, is not going to be supported (even though it is fully capable to).
Such marketing sucks ass. I already decided that I am not going to choose Onkyo for my next amp upgrade. And I might switch away from Spotify after paying them for 3 years too.
So yeah, fuck them - I'll do this stuff myself.
I was able to extract Spotify Connect implementation from one speakers manufacturer firmware, finally! (won't mention names for obvious reasons ;-).
So I am reverse-engineering Spotify Connect at the moment and it doesn't seem too hard. It is a relatively-simple protocol. Much simplier than what libspotify does.