There are already a number of Xbox games that support all those modes and they fit more than fine on a DVD9 (and some are pretty small, actually).
For example: Dragon's Lair 3D, Enter the Matrix, Syberia, MX Unleahed, etc.
Some were big (like ETM), and some are small (like Atari Anthology, that's hardly a space taker...
).
I don't think we'll have a problem with the next gen for awhile. But the time will come. Enter the Matrix required higher res textures, bitmaps, video, etc. and thus was large.