"it is possible to make the support for 32-bit virtual address space for each process to not to share same 32-bit space without any changes in instruction set?"
Yes. As you note, it's just entries in the task state segment descriptor (I think that is the nomeclature). Now there are some sublties that need to be taken care of by the OS, so there might be some problems that might make it more difficult at the systems level. And then there is the problem of the applications have to be changed to support the extra memory...
If Intel is going to support more than 4 gig. of memory except by PAE or an extended PAE, Intel needs to starting making that info public probably a year before they expect much in the way of support. We haven't heard anything about, so I strongly suspect that Prescott doesn't do anything really new. If it did, Intel would be mentioning it every chance they got, because that would eliminate the hole card for Opteron, addressing more memory and keeping x86 compatibility in the bargain.
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