Weaker online, graphics etc because the PS3/360 are less capable. They have less power so would be unable to do what Bungie might want to pull of.

Well yeah, the graphics won't be as nice on the older consoles, but I wouldn't call that a game feature. And that wouldn't mean having to diminish the quality of the next gen versions. Think about PC games that support a wide range of graphics cards. You're given the opportunity to select how detailed you want the game to look, so you don't overtax your graphics card. They could implement something like that, where on the old consoles, less graphics intensive textures and models are used, but on the new gen hardware, the full textures and models are used.

The PC example doesn't exactly fill me with relief considering how many times I hear about PC gamers claiming console are ruining/dumbing down PC titles too. A stronger online system is likely to come with the newer, more capable consoles. That would be something with more potential for features rather than appearance.