awesome im going to give it a shot ive been thinking a very similar thing!
How does it handle complex external hardware? That's where all the fun happens.
i put a post in gigs and collaborations for something im going to start working on in processing that will simulate
the target MCU'S output if a "hypothetical" pinout of basic digital components that can be determined using a database of truth tables for ICs that are designed as particular logic gates, but, as you said complexity is proportional to both fun of outcome AND mental strain achieving it, and there's a lot more fun than just ones and zeros to be had with other electrical components.