|Hopefully the games will look better than this mockup.|
When might this occur? As far as Apple goes, it could be any time. Logically they want to see it well in place before the holiday shopping season, so you might expect it to come this summer... maybe September. It might require a new release of Apple TV for the hardware to really support the kind of games you'd want to see. Maybe there would be more storage space, or storage options.
Google TV is undergoing a rethinking right now, and the implication is the hardware will be revised along with the software. Again, release before the holidays would seem like a bright idea, if the engineers can handle it.
GDC should be a good place to find out rumors. Apple and Google should be there looking to gain support from key developers.