When comparing
80486 and
Pentium 4, it becomes evident that their internal architecture is _very_ different.
They just both "understand" the 80x86 instruction set, and this might be all they have in common.
Same thing for
68000 and
68060.
IIRC 68000 used three PLAs for generating a 10 Bit microcode address from the OpCode,
but 68060 (two integer ALUs) internally translated the 68k machine code into 48 Bit RISC code.
So if you happen to have a fast
VLIW CPU and tinker a bit with instruction decoding etc.,
in theory it's not impossible to run 80x86 and 6502 machine code on the same chip.
But the problem is, that the 80x86 instruction set doesn't seem to make much sense, also it had evolved in a "natural way" (like tumors do).
Translating 80x86 machine code in real time certainly won't be fun, and the technical implications related to this might fry your brain.
It's a pity, that
Transmeta went out of business...
But back on topic.
Back in 2008, there was that TREX TTL CPU project, inspired by
Forth hardware CPUs.
There were 3 simple RISC instructions packed into a 32 Bit instruction word.Ok, the CPU only was able to handle 32 Bit data, one would need 8 Bit and 16 Bit data types, too.
Point is, that if there were 5..8 RISC instructions packed into an instruction word, one could
in theory use it as microcode for emulating
something like a 6502.
And with simple RISC instructions, checking dependency between them and making the thing superscalar\VLIW
in theory also
might be possible.
IIRC building that TREX TTL CPU took two manyears or so.
Hmm... not to discourage you, but for making up a "bullet proof" concept for 80x86, better expect this to take 100 manyears+ or such.
Good luck.