From a ZDNet interview with Dell:
ZDNet: Any thoughts on whether Intel will go the hybrid 32/64-bit route as AMD has with Opteron?
Marengi: Intel is there. I’m not saying that they have the technology ready or that I’ve seen it. But for them to put that technology into the marketplace would take a nanosecond.
That’s the most solid confirmation up to now that Yamhill circuitry is going to be found at least in Xeons and likely in Prescotts.
We repeat our current beliefs on this subjectWe think Intel is likely to implement x86-64 for at least some next-generation Xeons in order to better compete against Opterons in the low-end server line.We think the odds on more widespread implementation by Intel will be directly related to the difficulties Intel sees itself in ramping its CPUs over the next couple years. The more problems Intel has, the more likely it is to turn the circuitry.If this happens, we believe Intel will go with a version of x86-64 that is somehow incompatible with AMD64 in some form or another, most likely some sort of superset of AMD64. However, we suspect that any incompatibilities will be more official than actual; workarounds will be possible.We don’t think adaptation of x86-64 precludes the existence and continued development of IA64. IA64 will live or die based on how well it sells over the next 12-18 months. If it does OK on the high-end, Intel will probably continue to consider one of its descendants to become a desktop chip sometime towards the end of the decade.
One new thought:Should Intel decide on a Xeon implementation, it is now quite possible that we could see an “Extreme Edition” desktop CPU with x86-64 enabled, CPU manufacturing problems or not.
If any implementation does happen, it probably won’t start happening until about a year from now.