The mainframe is not a special thing anymore, hasn't been since the late 90s. It's just a server box.
I work at a shop with a z/14. I would love it if we finished the last COBOL retirements and go back to the mainframe but this time to run container farms, fresh Go code, and use thr power to run way deeper matrices of tests that take days to run locally and cannot afford to run on AWS.
Running x86 in z/VM has been a discussion for 25 years. Just fucking do it. Let people run whatever they want.
Just as people are excited about ARM for low-watt computing, make s390x just as exciting for people who want insane vertical resources but using the same dev tools that are used now for easy x86/ARM crossover.
But IBM culture has always been about overcharging a small and rich audience and now they are sitting around hocking their services cohosted thru AWS and everyone who has COBOL and 360ASM running are doing retirements with no plans to use the boxes after its all unloaded.
The funny thing is that AIUI the technology is already basically there. They actually did throw the resources into getting a lot of Open Source software to be compatible with s390x, they've got Linux LPARs and LinuxONE. My understanding is that they just... don't make any effort to sell, outside a tiny fraction of Enterprise™.