Needs microcassette drives like the original PX-8 (which I actually had for a time, although after it was discontinued and sold by liquidators for a fraction of its former list price).

https://en.wikipedia.org/wiki/Epson_PX-8_Geneva

It looks like there'd be room to stick one to the right of the screen, above the main board. I'd prefer a minidisc drive, though, to bring it into the 21st century.

My first thought too :-)