Well, Tim Schafer has been saying for a long time now that he'd want to do Psychonauts 2, but there have always been funding problems. However, now Markus "Notch" Persson, who became a millionaire through Minecraft, said that he wants to fund the game (and is serious about it).
Here's an article about it:
http://www.eurogamer.net/articles/20...-psychonauts-2
So, perhaps it is possible? Psychonauts definitely deserves a sequel, and has recently been getting some new publicity (for example with new releases on PC etc.), so this boosts the chances too.
I'm pretty psyched up about this!