Certainly, the higher video quality will require more capacity for the same amount of video, right out of the gate. But, I don't think it's necessarily going to require as much as HD and blue-ray provide, so hopefully, we'll finally get to use the "perspective" button on our future dvd players - where there are different camera angles, etc. that we can shoose from. That wasn't really possible with current dvd's because the average feature length movie was pretty close to the capacity of the dvd.
Then again, more and more crap is being loaded on to the dvds of today, like computer games, useless commentary, etc.
I am really hoping for a few orders of magnitude increase sometime soon, because dvd media is a really good media for backups, be even at 30GB, I'd have to use about 15 of them to backup my computer.