Assuming all three companies stay in the console business, and there are no new arrivals:
The only one I'm mostly sure about is that Sony will be using Blu-ray. The size will be enough for the foreseeable future, they already own the rights to it, and increasing the popularity of the format will always be in their best interests.
Microsoft and Nintendo will probably use something other than DVD. By then games will have reached the point where DVD size is limiting what developers can do, and everyone will be using HD anyway. Not sure if it'll be BR, since Sony might be a bitch about licensing fees, and the discs are way bigger than strictly needed.
Especially Nintendo doesn't seem to care about movie playback, so they could very well use a cheaper proprietary format with 2-3 times the capacity of DVD. Assuming they decide it's cheaper than paying up for an existing format of course.







