A lot of the stuff came from following the comments here.

I think it's pretty much a sure thing that KoL is playing (date still listed on their MySpace)...as for the rest, the Metallica one seems the most credible. What other event taking place over Halloween would they be willing to cancel shows for?

Last year they added NERD, Mars Volta and Lil Wayne (and close to 40 other bands) in SEPTEMBER. All of those are pretty big acts...so it's been known to happen!