It ought to go into modes for 6502 mode, 65816 mode, and 680X0 mode. Of which it would be compatible with systems that would use those sort of chips. Much like the 80X86 has 16-bit and 32-bit modes, etc.

I think since the 6502 was a clone of the Motorola 6800 series, just use 68K opt code for 16-bit and 32-bit modes. Make a 6502 type chip with the same pinouts and find an 8 bit 6502 system and swap out the CPU and modify the BIOS to work with the new 16-bit and 32-bit modes.

Either that or just ...