Just an update, I talked again on the scion.com chat, and they now immediately say that it is a mid-year change.

 

there are ways to make the steering wheel controls work with an after market deck. you get to benefit from the tCs who have been searching for a way to do this

there is an adapter, PAC SWI-X (using the '05 Camry instructions) that works well.
and the eclipse AVN2454 fit AND use the steering controls right out of the box.

if this works for the tC i don't see why it wont work for the xB/xA