The PSP2 rumor has been prevalent throughout most of the year, and it's most recently come to a fever pitch. Basically, the thing is coming…it's only a matter of when.
We've heard from one source that a few developers already have the PSP follow-up in their possession, and they're currently working on software for the new piece of portable hardware. Now, according to Develop , it seems the PSP2 is an inevitability and Sony is merely waiting to compile "a significant launch window lineup." This is based on information taken from "multiple industry sources;" the implication is that Sony "is spreading its PSP2 tech widely" so as to have a big impact when it hits retail shelves. By the way, if you're wondering, it probably won't be all-digital like the PSP Go; Sony boss Kazuo Hirai has since said they would not entirely abandon physical media in the near future. For the record, Netherrealm Studios' executive producer Shaun Himmerick told Industry Gamers that they have a "PSP 2 in house and we're looking at the engine."
At this point, it might be a good guess to say the PSP2 is set for a holiday 2011 launch, or perhaps even earlier.