I think we're making compatible points. You noted that you can bypass the OS by running on bare metal. (True! You can also use real-time OS features, devote one or more cores entirely to running the emulator flat out, write directly to a frame buffer - or maybe even generate the actual video signal[1], etc..) Another nice thing about a microcontroller board like a Pi or Teensy is that you can easily get signals in (e.g. controllers, keyboards) and out (e.g. sound, video) of it.
Note that Linux (which I'm familiar with) makes it fairly easy to bypass much of the OS for real-time applications, but you can get most of the benefit by simply running a single process (i.e. just run the kernel and a single emulator process.)
My point is similar to yours actually: that as long as you calculate the output signals on time (e.g. before the clock edge) there is not a meaningful difference between hardware and software implementations.
Note that Linux (which I'm familiar with) makes it fairly easy to bypass much of the OS for real-time applications, but you can get most of the benefit by simply running a single process (i.e. just run the kernel and a single emulator process.)
My point is similar to yours actually: that as long as you calculate the output signals on time (e.g. before the clock edge) there is not a meaningful difference between hardware and software implementations.
[1] http://www.radanpro.com/Radan2400/mikrokontroleri/rtvideo5.h...