Tech-wise places too much premium on the ISA. Modern processor design is fairly orthogonal to the ISA being exposed.

Intel could make exciting RISC-V relatively quickly if they wanted to; what stops them and other companies like this is the strategic asset they perceive their existing ecosystem as.

There's a nice interview with Mike Clark where he talks about this a bit. His take basically matches this. He says that, in his view, any efficiency benefits of ARM are just that's been the market for ARM. In his view, if x86 had a market motive for ARM levels of efficiency, they'd be able to deliver it. But, historically, the x86 market wants performance more than efficiency, so that's what it gets.

https://www.computerenhance.com/p/an-interview-with-zen-chie...

I don't think so. For example, if an ISA requires a strict memory ordering, this makes the architecture more complicated than an ISA with relaxed memory ordering, although the latter is a pain to write code for.