I have been suggested the following:

"When initializing the registers after a hardware reset, try to have the CPU hardware revision number in one of the registers. This way, if some instructions are missing or buggy in the CPU you have a fair chance of getting around this by software."

I much prefer the core's type, revision, capabilities etc. stored in ROM in the Special Registers (or IO) space because you don't have to reset the CPU to get the information :-)