Windows 8 might ship in 64 bit and 128 bit versions, based on the LinkedIn profile of Microsoft employee Robert Morgan:

Working in high security department for research and development involving strategic planning for medium and long-term projects. Research & Development projects including 128 bit architecture compatibility with the Windows 8 kernel and Windows 9 project plan. Forming relationships with major partners: Intel, AMD, HP, and IBM.

Robert Morgan is working to get IA-128 working backwards with full binary compatibility on the existing IA-64 instructions in the hardware simulation to work for Windows 8 and definitely Windows 9.

Hmm, very interesting…