Windows and x86-64 has way too much momentum for that to happen any time soon. What is going to be far more realistic is AMD/Intel making a new chip where they expose a better ISA and Microsoft releasing a Windows that support that ISA. All while keeping the tried and tested x86/x64 running in parallel and slowly allow software to migrate to the new ISA, or perhaps invest in a recompilation of executables targeting x86-64 to take advantage of the new ISA. But getting Amd, Intel, and Microsoft to agree on a new ISA is a tall order.
Windows on non-x86 would need to have emulation similar to Rosetta 2 to be viable, IMO. Over the past couple decades, we've had both Windows on IA64 and Windows on ARM releases, but they've never had much compatibility with existing software.
I'm not talking about a pure non-x86, but a hybrid chip that expose a legacy x86-64 ISA and a new and improved ISA for the future without all the baggage. Windows will have to target the new, and allow applications to use move to the new ISA at their own pace. With time they can make "Rosetta 2" style emulation with compilation to remove the old ISA all together.
That said I seriously doubt that the ISA in and of itself is the reason the chips are slower. After all, underneath is a state of the art architecture. Until I see a independent true cross platform benchmark in e.g. in dotnet be significantly faster and more efficient, I remain skeptical of such incredible claims.
