Could you make a small Power Driver brick that had just a motor driver chip inside it and took the C1 and C2 signals and replicated them with fresh power from the 9V and 0V rails at the output?
This would allow a single IR Receiver or S-Brick to drive many motors because it would drive only the motor driver inputs (low current x many drivers) and each Power Driver brick would apply the motor current from the power rails to its motor.
I would like this for Trains and Technic where two motors are not enough for the high power the model needs. Some of my trains use 4 train motors plus gearmotors plus lights, a total current of 1.3 Amps. I would like to use 1 battery box per vehicle (1 in the engine, 1 in a coach) and the same electrical control signals on C1 and C2 from an IR Receiver or S-Brick to control all the motors with the same signal. This would need 2x Power Drivers in the coach and 2 in the engine.
The Power Driver would get over the problem of using 2x IR Receivers on the same channel when one misses the IR signal (perhaps when the train is partly in a tunnel), a situation that may lead to derailment. It woud be useful for stateside trains with an A-Unit and many B-Unit locos.
The design of the Power Driver may have a flying lead input or may have a socket on the bottom of the brick as the S-Brick does. The single output to the motor would be on the top. I wonder if it could fit in a 2x2 brick, or whether a Technic hole attachment would be a useful addition?
The ability to take the signal from one source and the power from another may need a split PF lead - this could be another standard product in your range.