Question is, why is it only "next" version.
Almost all new processors are 64bit, infact the only processors sold in the past 2-3 years that are not x86_64 compliant have been the Intel Core Duo / Solo - which are bargain basement as it is.
AMD have had x86_64 CPUs since 2003 I think, and have not sold a 32bit one since 2005.
Even the Atom is x86_64, so I think Windows 7 would have been a perfect time to dump 32bit (to be fair Vista would have also been a perfect time).
[EDIT]
Having said all that, there is no reason why 32bit version should not be released, afterall look at Linux, it manages perfectly fine to have a 32 bit, and 64bit, and PPC and ARM and <insert another processor type> version.
The only reason for MS to dump 32bit version is to force evolution in the software market place, forcing companies to create products that work with 64bit (for instance SolidWorks 08 had plenty of issues with 64bit and Vista, as did Autocad).
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