Personally I’d want just to connect two standard keyboards. One for each hand. But then I’d need a keyboard driver that will let the shifting keys on one keyboard affect key actions on the other keyboard. Is it hard to write my own keyboard driver?
Also, having two "half-keyboards" takes up less space than using two full ones.
Re: the driver, it's not terribly hard to get the basics working (debouncing, matrix scanning, etc), but you'd probably be better off using QMK, since it's well tested and has pretty much every feature you might need, and then some.
But actually it was the OS kernel keyboard driver I meant.