Seeing as BT and Sony have recently announced a deal to turn the PSP into the phone, a redesigned unit that is a tad smaller with a built in mic seems the most likely route to me, though whether that is what the customers are after is another thing altogether.
To be honest, besides the battery life I am quite happy with mine. There are of course things I would like Sony to do differently next time around but at the moment I want some sort of unified online service much more so than I do a new unit.
I am thinking more demos more often, lots of cheap PS1 emulation games (and possibly others too ie amiga, atari etc) video on demand, and a fully integrated online gaming service that basically abolishes all ad hoc games (am I the only one who thinks the odds of meeting someone on your way to work who is packing the same game and wants to play are extremely small?)
If Sony could do all that and offer it wirelessly I would be an extremely satisfied PSP owner as opposed to just a satisfied one.
My two cents...