The dev alpha device already has a greater resolution on a smaller screen than the PlayBook. 1280x768 I believe. It seems like that may be the universal screen resolution for most of their phones (and probably the PlayBook)
That's the natural evolution of displays, higher resolution, so I'm sure it will be improved at some point. But in the case of the PB, I actually don't care as it has such a beautiful screen now, much better than most displays out now.
FWIW it's not just the resolution that gives you a good display but the graphics software and processor. That's why on the iPad3 they had to go with a quad graphics processor to work with the higher resolution screen. The iPad3 main processor is still the same as the iPad 2, dual core rocessor, but the graphics is quad. IPad3 is still a true dual core, not a four like some claim. Same goes for your PC display. Without a good graphics card, that HD screen won't look that hot. It's also about doing with what you got.