ISA doesn’t matter as much as most people think it does. It’s all about how you implement it.
How do you hire people who can implement it right? There are three companies that can make x86. One is failing, one gave up years ago, and the third is kicking ass but seems uninterested in this part of the market. All the people who know how to do x86 well already work for one of them. That third company that nobody talks about gave up because by 2010, they lacked the ability to make a worthwhile product.
It’s an incredibly difficult ISA to work with, and all the talent is already busy. Due to its closed nature, there is little hope of significantly growing that talent base. Not unless you want the early 2000s version of x86-64, which is patent free.