Microsoft built Windows kernel to have different backends (Itanium, ARM) and different front ends (Win32, Windows Subsystem for Linux), they make Hyper-V and did a "run your old apps in a Win 7 VM" for a while, they've pushed .Net since the early 2000s where the intermediate code isn't so tied to hardware. They could plausibly have done something for compatibility like Apple does with Rosetta.

Thing about your comment is "Who would buy it" assumes it's basically the same and people are indifferent. My griping is assuming ARM is generally worse. But if we take this alternate world seriously then the reason for ARM is superior performance, so the answer to "who would buy it" and "why would developers switch" is driven by that - like when Apple was falling behind with PowerPC - it wouldn't be Microsoft pushing it on an unwanting market, it would be a demanding market pulling it with demand.

If Samsung could push a better-than-Intel chip, would Microsoft not want a piece of it?

If Samsung Chromebooks were suddenly more powerful than an Intel i7, would developers not sit up and take notice?

My contention is they can't, because ARM isn't that different, and it's Apple's black magic that is the real difference.