I doubt you will see a redesign soon. They seem pretty content with the current design of the pro machines. The only thing I would like to see changed aesthetically is getting rid of the latch and going to a dimple like the MB but because the case is metal I think it would be too much trouble to try and get it to look good.
I dunno, I think it's about due. I'd expect it to remain Aluminum. Maybe it's just wishful thinking, but I'd like to see the MBP be able to swap the HD out as easily as the current MB range can -- seems to odd that the consumer notebook gets that when the pro doesn't...
The other thing that springs to mind is IF they do go to LED backlit displays, the lid could be a lot thinner, and thus the body could be thicker while still keeping to that fabled 'just 1" thick'. That in turn would allow a better GPU, a bigger battery, a standard height (and cheaper and faster) DVDRW drive, etc. -- of course, it could look pretty much the same and just have relatively minor proportional differences too.
One reason we've not seen much in terms of case redesign is Apple presumably chose to keep existing cases for the most part as they moved the guts over to x86, presumably to ensure people still thought of the new hardware as "A Mac".
I figure we'll start to see new "different" designs on at least some systems by the end of 2007... tho it could be the iMac that changes first, not the MBP.