After actually doing some research on this, I have changed my mind. I say R4 should only be out on PS3 and PC.
A dual-layer PS3 disc holds 50 GB. A dual-layer Wii disc holds a mere 8.5 GB, and a 360 disc holds 9 GB (not sure if that's single or dual). A PC disc's storage capacity really depends, I guess but it could probably hold quite a lot.
If R4 is anything near what I want, it will not be compressed onto a puny DVD-ROM. Toning down the graphics isn't good enough; there will be more to this game than graphics.
Anyway, if it's out for PC, you'll all be able to play it, so who's complaining?