As much as I had been resisting a fruitless exchange of conjecture (I imagine John and Kevin blinking furiously at the thread wondering why we waste our energy), I admit that it's still entertaining!
I agree on Disney not renting out Pandora right away (or rather, I'd expect them to be running their own special events), so if we got in to Pandora after hours it'd only be because there was some special event already happening.
I still personally am thinking Epcot since Epcot's closing time never (rarely) changes, so the contract would be easier to draft up. Magic Kingdom's hours--being more fluid from week to week and often being extended in the weeks/days/hours leading up to a particular day, especially during busy periods like the end of May--to me makes it seem less likely that they would contract out an after-hours, in-park event there.
Future World seems like it'd be cheaper to staff a limited-access zone, especially if the Land pavilion wasn't open. And you could throw some cupcakes on a buffet table somewhere pretty easily. Plus, Epcot fits into my touring plan better. And as much fun as a 12a-2a (estimated) party in the Magic Kingdom could be, I'd be rubbish the next day (not that I wouldn't be willing to fall on that sword!).
