This is what Intel attempted with Itanium. The hardware implementation was too slow so they pulled it.
More recently is Nvidia's Denver project, which has a private ISA and dynamically translates ARM instructions. It's an open secret they had it working for x86 too, but it was scuttled due to patent threats.
I suspect they never shipped the x86 version because it wasn't competitive. Nvidia's CPUs couldn't keep up with contemporary Arm Cortex parts (probably a good part of the reason they bought them), let alone Intel and AMD stuff.
More recently is Nvidia's Denver project, which has a private ISA and dynamically translates ARM instructions. It's an open secret they had it working for x86 too, but it was scuttled due to patent threats.