My two cents' worth:
I've been looking to replace my 15" G4 PB and was tempted by the new 15" SR MBP, but I decided long ago that my next laptop would have to be smaller and, most importantly, weigh a lot less. I've been traveling more lately, and lugging that hunk of metal around the world (in addition to all of my other luggage) is just too cumbersome. And no, I'm not a 98-pound geek, I'm a stronger (and bigger) than average guy. Not only is the 15" form too heavy to carry for hours, but it's also too unwieldy to use in tight spaces like an airplane seat tray. I also like to work while lying down (and I bet I'm not the only one -- not good for my back to sit all day), and trying to balance a 15" 5-1/2 pound laptop on my chest isn't fun.
So, my hope for the smaller-form MBP is that it will weigh a lot less than any current Mac laptops. But I wouldn't want it to have anything less than a full-size keyboard. As far as I can tell, that means it shouldn't be smaller than 12". I'd almost prefer a 13" model, frankly, if the extra real estate doesn't mean more weight. (Maybe it can be thinner, then.) And I want it to be a full-fledged computer, with at minimum the same capabilities as a current MacBook.
I don't care, however, if it has an optical drive, I'd easily give that up in favor of less mass. You can always get an external DVD drive for those very few occasions you absolutely need it, perhaps Apple will make a really cool sleek one to go with. I'm more concerned that it has decent graphics capability, if not quite up to current MBP standards, at least better than the MB's. I don't even expect a massive hard drive, I'd settle for a smaller one (maybe 60 or 80 gb), once again, if it means less mass. (And, once again, if you need it, you can always get an external HD.) A SSD would absolutely rock. Not sure what a touchscreen would add other than wow factor, but I'm willing to be wowed.