let me set the record straight: (as far as the rumors go) they are making a PSphone, but it is not a psp2,
it is a sony phone (that is almost as powerful as a psp).
they are 2 different devices, its like calling the psx the ps3. IMHO
now, lets talk about the psp2, as a hypothetical device, and keep the rumor talk a little on the low (in other words, try to keep any non factual information about the proposed successor to the psp to yourself).
I strongly believe that if Sony released something like that, they would try to make it backwards compatible (one of the things that made the ps2 big was that it had backwards compatability), with the psp software. assuming it wasnt possible to do that, would minis still be playable on it? absolutely!
sony demonstrated a major thing with minis: that they are working on a psp emulator, but cannot effectively emulate games that use the full strength of the psp.
hence minis being playable on ps3, they are a line of games that are so simple that it is possible to emulate them with ease! for proper emulation of "real" psp games, the psp hardware would be the only way to do such a thing while guaranteeing no problems. I strongly believe that these facts can be applied to the ps3 or hypothetical psp2 (which, it can be assumed would be somewhere between a ps2 and a ps3).
I fully expect a tiered Minis platform to launch with the next PSP. One tier would support PSP/PSPNext/PS3 (this would be all Minis released prior to the new PSP), the next tier would support only PSPNext/PS3. The new tier would likely have it's own sub tiers as PSP Next has got to have a touch screen, and that would make it incompatible with the PS3.
that is quite likely, bravo for being the first to suggest it here.