Also is it possible that Skyrim or any future TES game would be so massive it would be released on two discs?
I actually asked this myself at one point. The question is, with an open world game, where would you split it? In a game like ours, you're constantly bouncing all across the map, so it's not like there's a natural place to gate the second disc. (And if you had to swap discs every time you crossed an arbitrary line in the world... ouch.)
If you think about games that ship on multiple discs, they're all either very linear or most of their asset usage is. Since you could encounter (for the most part) any piece of content in any order, we can't predict when a good time to do the disc swap would be.
Excellent question.