Hi,
If you want to go even more retro. Check ROM BASIC I extracted from old 286. I programmed a ROM loader to it, so SeaBIOS can load it from misc/
http://assembler.cz/rombasic.rom
This is a complete ROM already. I have even an MP3 with cassette recored of IBM diag tools, which I converted to ROM + implemented a cassette BIOS patch.
This can be loaded from fake "rom" which emulates the cassette in the ROM basic.
If anyone is interrested I can send to anyone.
Thanks Rudolf