Yep, this won't play as an option for the top row of keys inside an iOS 8 keyboard extension. There is no method to display art beyond above the area where the default view of the keyboard resides.

Obviously, Apple doesn't have to play by their own rules... but I understand how this could be abused.

The CYRKeyboardButton seems like a great starting point for someone building a keyboard native to their own app or if the art is used on the lower rows of keys.