Is that you Ash?

Come now AC, I suspect you are being intentionally obtuse. Of course Intel could have come up with some sort of 64 bit x86 architecture by themselves (if they cared about their installed base and had actually wanted to); but as you said, they already had the IA-64 monstrosity. AMD did us all the service of providing an acceptable alternative to Intel's plan of forced obsolescence. And, technically, AMD64 turned out pretty well, not sure IA-64 would have done the same as the only desktop\server ISA as it looked like things were headed.

https://en.wikipedia.org/wiki/...
"AMD64 was created as an alternative to the radically different IA-64 architecture, [by Intel and HP]. [...] AMD64 architecture was positioned by AMD from the beginning as an evolutionary way to add 64-bit computing capabilities to the existing x86 architecture, as opposed to Intel's approach of creating an entirely new 64-bit architecture with IA-64."

https://en.wikipedia.org/wiki/...
"but with x86-64, roles were reversed: Intel found itself in the position of adopting the ISA which AMD had created as an extension to Intel's own x86 processor line. [...Yamhill] After several years of denying its existence, Intel announced at the February 2004 IDF that the project was indeed underway"

https://en.wikipedia.org/wiki/...
"[...] Intel had originally hoped [Itanium] would find broader acceptance as a replacement for the original x86 architecture.

AMD chose a different direction, designing the less radical x86-64, a 64-bit extension to the existing x86 architecture, which Microsoft then supported, forcing Intel to introduce the same extensions in its own x86-based processors.[15] These designs can run existing 32-bit applications at native hardware speed, while offering support for 64-bit memory addressing and other enhancements to new applications.[6] This architecture has now become the predominant 64-bit architecture in the desktop and portable market."