Intel's has one ultimate problem: the X86 instruction set takes too many transistors to implement.
Everything about the modern X86/X64 architectures from both AMD and Intel shows just how clunky the instruction set is. The pipelines, instruction decoders, branch predictors and caches that are needed to make x86 perform well take an enormous number of transistors. Both Intel and AMD have done really well to make it work as well as it does, but the efficiency is low.
Whereas the ARM instruction set is far simpler to implement to perform well. Memory, modest cache, simple pipeline, CPU core, job done. That means less transistors, which means less power, etc. etc. The only reason Intel are still 'ahead' is because they're so good at making transistors, disguising their architecture's profligate use of them.
So as soon as Intel lose that silicon processing edge, they're doomed. ARMs can nip in and perform just a little bit better, and that's the server market gone ARMwards. There's not a lot they can do about that. The world didn't like Itanium. I doubt there's room for yet another CPU architecture. They could build their own ARM based CPUs, and they'd likely be the very best that you could buy.
For those of you muttering about MS being left behind - don't forget that at some tech shows some years back they showed desktop Windows working on an ARM board running Office and printing. If that's where they could get to with an experimental Alpha build then I don't suppose that porting Windows server is going to be that hard. Probably the biggest portion of the job is verification & testing.