I'll be especially interested if jailbreak apps make the cut. I think that will be the real iron test of this system. Will Apple allow through a non-malware app that goes directly against them? I'm not going to bet either way on this one, but I hope someone makes them choose.
I'm also interested and have submitted a request to FireCore who provide a jailbreak for Apple TVs. Their bug tracker also indicates that they were considering signing recently.
I have not received feedback, yet, but will monitor this closely.