Gamecube disks are 1.5GB, so depending on the size of KotOR 2, it could be 2 disks, which is not unheard of on Gamecube. One of the Resident Evil games was produced as a 2 disk game.
I think the thing that prevents a port to Gamecube is the differences in the system. An Xbox is really just a stripped down PC, as evidence by the fact that many people have hacked them and added Linux.
Gamecube uses a lot of proprietary stuff, built for them by ATI and IBM.