Don't get too excited OR too disappointed: Notch says that plans to fund Psychonauts 2 are undecided at the present time.
The creator of Minecraft famously tweeted that he would be willing to throw money at Psychonauts 2 in order to get the game made, which he revealed was a semi-joke. At the moment, he seems to be fairly serious about the project if everything works out, but things are currently stalled due to the Double Fine Adventure project that was recently raising record-breaking millions on Kickstarter.
Speaking with Digital Spy, Notch said "I meet with Tim [Schafer] at GDC, and basically what he said was, well now we've got three million more dollars here [for Double Fine Adventure]. So we're going to be busy for a while."
"I said we also didn't realize how much money you'd need. We discussed different ways it could be funded, but I still think that would be a very interesting investment to make, but we haven't decided anything either way."
So as of now, the project is on hold. However, that doesn't mean it will never happen. Notch is still interested in pursuing the idea again at some point in the future. So hold your excitement for a few years, and maybe this is something that will sneak up on us again!