Well it depends, All ECUs are capable of sending something to the sport monitor, there are cases where only a gateway will solve the problem and in other cases ( usually on smaller engines) both ECU and gateway are the problem.
Retrofitting 3Q0 gateway just for sport display is nuts. on the other hand, if you are constantly looking for something to retrofit, a 3Q0 gateway would be a great idea, will make sure all your retrofits work well even if your car is old.