There is a datasheet out there for the 32-bit successor to the 65C816, the never-produced 65C832.

https://downloads.reactivemicro.com/Electronics/CPU/WDC%2065...

Has anyone ever written an emulator for this? I am no expert on this but isn't there enough info in there?

It could be run on a $5 Raspberry Pi Pico these days, and used as a plug-in accelerator for a 65xx system. (Akin to a PiStorm.) Maybe someone could even do an FPGA version...