Blu-ray for pretty much all, unless they don't manage to get more layers working at a decent price. That is, they might have to put in more space if this gen is going to last long. That, of course, depends on the hardware, and current BDs are probably enough if next-gen console won't have significantly better hardware. Anyway, BDs have a lot of potential when they have several layers - 200 GB (done already, I believe) ought to be mostly enough.
And not using much better hardware wouldn't be because of Wii - it would be because of ridiculously high development costs.







