I've had this theory that the current gen handheld game systems were a bit of a testing ground for the then next generation home systems.
I also feel some what vindicated with what we ended up with (Look at the ds and then the wii. Both radical departures from the traditional with the touch then motion controls. With the psp and the ps3 I saw that more as a proving ground for the xmb and various media functionality, not to mention local storage media in addition to the game media. Anyway...). Now it seems Nintendo has teased the Nintendo 3DS - and Nintendo has gone on record as feeling that a Wii HD isn't a big enough innovation to make next gen hardware.
A Wii 3D on the otherhand? Nintendo is flush with cash and crazy enough to try it.
I wonder what Sony has in store for the proper PSP sucsessor? (well, besides a ps3 style hypervisor hah!)