Well, you can already do things like this, eg emulating x86 on some microcontroller. But the problem tends to be that the emulation runs magnitudes slower tha

Well, you can already do things like this, eg emulating x86 on some microcontroller. But the problem tends to be that the emulation runs magnitudes slower than the new hardware, so it is impractical for almost every use case beside Doom ports to exotic hardware.