If Apple ports UIKit to Lion, the API side of things could be very easy. The big challenge here is in interaction design.
Some games might make the transition relatively easily. A game that relies mostly on single points of touch has a somewhat decent analog with the mouse, but only if it relies on certain patterns of finger movement. A game that, for instance, involves alternating taps on opposite sides of the screen, would translate badly—it's nowhere near as easy to leap that distance precisely with a mouse as it is with your fingers. Can you imagine playing the iPhone classic Dactyl with a mouse?
That kind of difference is present all over in touch-based applications, in differing amounts. It's up to the developer to find what transitions well and what doesn't, but in most cases it won't be a trivial task.
Touchpads are not 1 to 1 though, like wacom tablets or touch screens, you still have to "move" the mouse, you can't just touch where you want it to go.
OK, so I'm totally ignorant of workings of trackpad (or its potential to work in ways additional to its current use), but might it not be possible for Apple to add the capability (via software) to enable tapping on left/right edge of track pad to have trigger events that are triggered by touch to left/right side of an iPhone/iPad screen?
I have actually searched for alernatve divers for my touchpad (on a pc) to do this, with no luck. I am sure it's possible though, the only limiting factrs would be the accuracy of the touchpad, and users unfamiliar with the new mode.
Some games might make the transition relatively easily. A game that relies mostly on single points of touch has a somewhat decent analog with the mouse, but only if it relies on certain patterns of finger movement. A game that, for instance, involves alternating taps on opposite sides of the screen, would translate badly—it's nowhere near as easy to leap that distance precisely with a mouse as it is with your fingers. Can you imagine playing the iPhone classic Dactyl with a mouse?
That kind of difference is present all over in touch-based applications, in differing amounts. It's up to the developer to find what transitions well and what doesn't, but in most cases it won't be a trivial task.