By 2012 there will be a new Nintendo handheld, a new Sony handheld and an improved Apple handheld too. I reckon Nintendo will be the last to release new hardware, the DS is still doing extremely well and I personally can't really imagine where Nintendo would take the hardware next. The DS is exactly fit to purpose as it is and I don't think improving the platform's graphical performance will be a priority.
The PSP2 will almost certainly be a more powerful beast than the current device, but besides new interface options, I think Sony will look to other ways of improving its handheld offering. To be honest, I think it's the business model that's going to change more than the devices, I think we'll see both Sony and Nintendo adopt aggressive digital download strategies similar to the App Store. The benefit here is that both companies, unlike Apple, have such a rich history of titles to sell on such services. For that reason, I expect both new Sony and Nintendo handhelds to have control systems that would make ports of PS2/Gamecube era titles easy to achieve (and hence ports for games on platforms prior to that era easy too).
As for Apple, I think we might see a handheld that doubles as a home console in some way. Perhaps something that can interface with Apple TV wirelessly in order to deliver big screen gaming via a portable device. I don't know if going more powerful would be a good idea, Apple's current business model and hardware allow developers to create games on a reasonable budget quickly. Upping the scope for complicated in-game assets might strangle and slow down the development process and my money is on Apple adopting the strategy that allows them the quickest short term growth in the games market.
Like a tramp in the night, I'm begging for your love - Samantha Fox