In a mix of speculation and rumor, Ars believes that Apple will stick with Intel chipsets due to upcoming Intel-unique technologies such as Nehalem and its upcoming QuickPath interconnect and Larrabee, a forthcoming multi-core GPU from Intel.
And I've heard from a source that I trust that Apple will use Larrabee; this makes sense, because Larrabee, as a many-core x86 multiprocessor, can be exploited directly by GrandCentral's cooperative multitasking capabilities.
Not much has been officially revealed about Larrabee, however various leaks documented on Wikipedia have suggested that the GPU would be a competitor to NVidia and AMD/ATI's general purpose GPU (GPGPU) offerings. The chip could see a Summer 2009 release in 24 and 32 core varieties with performance perhaps reaching up to 2 teraflops.
Reminder: Chipsets are the chips that accompany a CPU. Apple could stop using Intel chipsets but still use Intel CPUs