There isn't a screen available that would fit and be as good as the current one, the only one I'm aware of, which is 256k colours only, is pretty expensive - and would still require a complete case redesign.
The current case creaks, cracks and rattles. Frankly, I would put that towards the top of the 'redesign list' for a P2 anyway. Rebuilding the case to match a bigger/better screen sounds like a win/win.
Well the Pandora2 should be the best it can be, and that will be the goal.
The P1 was very ahead of its time when we first started, we were then unfortunately held up by the fact what we were trying to do was seriously complex.
The P2 won't be held up like that, we know what we need to do and the best way to do it now.
So we can seriously launch something to rival the best hardware on the market.
This device revolves around it's screen. Don't skimp there - raise the price if you have to, but with current device trends (iPad 3, Galaxy Note) toward extremely high pixel density and larger screens in portable devices - you don't want to be stuck at 4.3" if you can do 5"+ and still maintain a pocket-able clam shell device format.
Start with finding the ideal screen - then build the device around that. If you think 800x480 is the best hardware on the market, then you're out of touch.
Galaxy Note: 1200x800 at 5.3".
iPhone 4s: 960x640 at 3.5"
Your keymat is great - keep it.
Your nubs are great - if anything, make them socketed so it's easier to repair/replace them.
Clam shell design - winner.
Audiophile amps - must have.
Dual full size SD slots - make it 3 with one behind the battery and skip the NAND. Need to be capable of 100MB/sec read.
Shoulder buttons - get rid of the two giant flapper paddles and put in four (two per side) real buttons - slightly recessed. You could use the same molds as the AXBY buttons minus the letters - and two small circuit boards mounted vertically to house the contacts.
Case plastics - starting over is NOT a bad thing here. The quality of the existing plastics - we all know it was a compromise and the costs are important, but I'm on my 2nd case and it's already separating again and it's only been in service 11 months. Completely new plastics for a P2 is a GOOD idea.
IMHO