If it happens, it'd be Halo month, though I suspect even halo won't provide a HUGE surge. Halo fanboys have consoles already. A limited edition model with Halo might spark some sales, though. Like a Halo model with H3, ODST and Reach all included?
The only other chance would be more supply constraints for the others or if Natal somehow is some mind-blowing mass-market phenomenon - the Tickle-Me-Elmo for the holidays. I personally don't see that happening ever, though - especially at its launch. I suspect the early games will be kind of lacking.