I had a little time to work on that today and managed to display something
I don't know exactly how much the SH-1 could be used, but it could certainly handle the cartridge interface and probably also mapper emulation (incidentally, it has 512kb local RAM, and guess how big NES's biggest games are?).
PS1 isn't a good comparsion. PS1 just doesn't have the CPU muscle of Saturn, and it has half the usable RAM
PS1 has 2MB total.