The A1200's keyboard interface is not a difficult thing to adapt to the Minimig. If there were a decent market, could make custom minimig boards. If not, can do an A1200 to PS/2 adaptor. Either way, piece of cake electronically. Anyone with 15 minutes could whip up the schematics needed based on the numberous PS2 to Amiga adaptor schematics from Aminet.
The keyboard controller for the A1200 is not on the keyboard, it is on the motherboard. PS2 to Amiga adaptor schematics won't help you at all.
An A500 keyboard, on the other hand, would be easy to use with a MiniMig.