I think up until the 3DS, console hardware was still somewhat specialised, to the point where you can’t 100% accurately emulate old cobsoles. But at the level we currently are, consoles a little more than all-purpose computers. Emulating then is only down to having enough computational power.
A lot of old consoles are actually based on standard CPUs for the most part. Look at the history of the 6502 for example. Emulating the hardware can be done if time is taken to reverse engineer all the layers into an emulator.
Part of the issue, to me, can be if all the work is done and then copyright disputes arise- all work has to be removed from the public.
At this point you can write the circuitry in SPICE and the chips in Verilog and simulate the whole old console clock by clock down to the transistor level and still get a playable game out of it
Of course this is only viable until say… before the 3D era or so