To be honest the only reason to release a new one this year would be if it needed the dual core A5 to run apps, add 3D movie support or 24p support comes along. As it is the current model is capable of decoding all 1080p thrown at it and the A5 is still used in many shipping products (iPad 2, iPhone 4S, iPod touch, iPad mini) so no issue of supply.
A release next year would allow h.265 decoding hardware to be included so Apple could squeeze even more quality out of the bitrate. At this point nothing would surprise me but I'd much prefer to see a decent software update.