The Poker II has such approach, though the custom made ones uses tensy board with an AVR ATMEGA32U4 8-bit microcontroller and other similar micros, that allow actual programmable capacities. If some keystrokes are enough for your needs the commercially available keyboards may serve you well, but if you need full customization you may consider the current GB that Sprit is running. It has many options from 60 to full size kits with actual programmability.