The new Halo will run at 60fps; resolution is at this time unspecified but there's a good chance it won't be 1080p. This represents a 2x to 4x increase in number of rendered pixels already, so there's about 2x-4x rendering performance left to utilize at most (and I doubt that they'll stay at 720p, 900p is more likely). If they simply just max out what the current renderer can do (proper shadowing, lighting etc) then it's already about as much as the hardware is capable of.
Of course the heaps of extra memory will also be spent, on more textures, more detailed meshes and probably more enemies in large scenes, too, but apart from that I don't really see much need for new developments.
Which was probably the idea anyway - 343 has 2 years to produce the sequel and that's not much. So they developed a lot of tech that was meant to be scalable to the new platform, like their facial animation system (not much is known about the rest of the engine, except that it's mostly based on the H3/Reach engines). They've also layed down the groundwork for the Forerunner race and have enough conflict to last them for the rest of a new trilogy.
Of course the heaps of extra memory will also be spent, on more textures, more detailed meshes and probably more enemies in large scenes, too, but apart from that I don't really see much need for new developments.
Which was probably the idea anyway - 343 has 2 years to produce the sequel and that's not much. So they developed a lot of tech that was meant to be scalable to the new platform, like their facial animation system (not much is known about the rest of the engine, except that it's mostly based on the H3/Reach engines). They've also layed down the groundwork for the Forerunner race and have enough conflict to last them for the rest of a new trilogy.