If they do redesign the case, and I'm still not convinced that they will, it will be for usability purposes, not to make it pretty or small just for the sake of it. When you open up a Mac Pro, and really, you should, they are gorgeous inside, you can tell they were designed to be used, not look pretty on the outside. Inside they are neat and organized, and a dream to work with. When they're running, they are quiet and cool, with ports organized in a logical way. The original G5 cases were excellently designed, but they've only gotten better.
Apple won't retreat from the current Mac Pro case. They might, if they can figure out how, advance to something better. If the internals start using less power, and don't need as much cooling, and Apple expects that trend to continue for the foreseeable future, Apple might start moving to a smaller case design. As much as I'd like to think SSDs will be small enough, cheap enough per GB, and standard, so that Apple can stick 4 SSDs in there for less space, I think we're stuck with four large HD bays. Pros need all those bays, though, so don't think they'll drop down to 2 HDs just to get a smaller case. I do think the Mac Pro will be the last Mac to have optical drives still on there. Pro Macs always are the last hold-outs for obsolete technology (not that optical discs are quite there yet, they're getting close). I remember SCSI cards being an option in the Apple Store for the old G4 PowerMacs for the longest time, even as everything was moving to FW400 and USB.
No doubt Apple would love to reduce their aluminum and shipping costs by making a smaller case Mac Pro, but they know their market. The Mac Pro market needs all the stuff that's in those current cases. Until they can figure out how to shrink those internals, and maintain the same functionality and usability, Apple won't change the case. I don't see a radical change happening soon, but maybe they will reduce the size slightly, internals allowing, to make it more easily rack-mounted.
Anyway, it's fantastic news hearing some hints of a new Mac Pro model. I can wait, but not too much longer.