Turbo Kernel

To this point, focus has been a thought experiment over the hardware. No kernel exists. I haven't even begun to evaluate this to know if there might be kernels available, but given I haven't found any bare-metal RISCV style computers of the kind proposed, this may need to be a greenfield design.

It would be one that borrows from Commodore style systems, or more specifically the Commander X16 which is a quirky hybrid given there exist DOS and Unix like shells for it (such as x16-shell). I personally am not particularly fond of BASIC and while I'd be completely open to having a BASIC option, my interest lies in writing assembly programs such that the command-line UI will be very basic (not BASIC) less someone comes along to work on a full BASIC.

BASIC or not, there needs to be a number of system calls to make the system useable by a programmer. Default ISR, Keyboard handling, File I/O, if not basic some sort of CLI to run programs easily by the user, etc.

Being a baremetal machine, if someone wants to write a more complete OS, cool beans! But the purpose is really for programs to be able to exert full control of the system in proper retro style. There is not any distinction between OS and programs, no safety-net, etc. By design.