I am investigating the change in bed size for the TAZ6 to 300 x 900(y). What will have to be done to the Firmware to make this happen.
It depends on how you handle the hardware and the thermistor placement. A 300 x 900 bed is going to require more amperage for the heater than the stock Rambo board will handle, so you would need to put a relay in line, probably using a dedicated power supply. You also may have to go up to a NEMA 23 motor size. So you may need to change the motor firmware, but the bed wiring would just trigger the relay and heat via that anyways. If you are using the auto leveling you would also need to change the bed size, bed auto level washer target positions, etc.