1. Possibly in an update
2. Not likely, but more likely is a 250GB option
3. Apple won't add this, but there are hacks available
4. Nice idea, but it isn't apple's vision of the future. It would make things too complicated, and draw people away from iTunes store.
I have an idea that might happen - iTunes WiFi Store for AppleTV, they added it to iPhone, so why not this? Buy videos and movies on the TV, and they will sync with your iTunes account wirelessly. Buy stuff from the comfort of your seat.
I'm not excited about that feature, but it seems like a logical move to me.
1. Seriously doubt 1080p with 5.1 due to file size of downloads. For 5.1, there are really only two options - Dolby Digital or DTS. There are no consumer-grade receivers or amps that can decode anything else. This also means an increase in file size for downloads. The H.264 files would likely be about 2.5 gigs with 5.1 audio using standard DVD size. Make it 720 and you'll probably increase that to 4 gigs.
2. Nice, but probably won't happen.
3. Again, nice, but unlikely since Apple's pushing H.264 with Quicktime. If Apple would open up the ATV for third-party development, then I suspect these would come rather quickly. But it will have to be via Quicktime, unless the make Back Row use others.