Sony files series of patents for two-finger touch devices
Other suggested layouts in that application include a hypothetical design "wherein the first and second case portions are slidably connected to each other" and one "wherein the visual display and touch pad are disposed on the same side of the case." In fact, Sony covered its bases, listing every possible combination of screen and touch interface as a possibility.
Other patents deal with specifying a "buffer" region on the touch interface between active input areas, using touch on one input to activate zoom on the screen, and highlighting information on one screen in response to a touch, in order to disambiguate. It sounds like Sony is most interested in using touchscreen input to affect a separate display, which would suggest the rear-touchpad interface from that purported PSP2.