128-bit? No one (and I mean no one) in the x86 space is moving for 128 bit. I don't think anyone is mass producing such CPUs, there's no point. 64 bit ints give you something like 10^19 worth of space, SSE registers are already 128-bit and being used extensively. It's not the next natural step in any sense. Even if you were right, they're more than capable of porting Windows; they got XP running on both Itaniums and AMD64, and the 32 and 64 bit branches of Vista and 7 work fine.
Besides, their track record so far is to use a kernel for as long as they can. 95-98-98SE-Me, NT-2k-XP~Vista-7-8(presumably). There's nothing in 7 so far that would force them to abandon the NT kernel, unlike the little shop of horrors that finally killed 9x.