LowNSlow
I agree that Mode C would be as good for the TCAS purpose.
However an elementary Mode S XP doesn't need the inputs you mention. It is a straight replacement for the existing XP, if you have one.
Only an enhanced Mode S XP needs them, and they don't apply to GA. Which is just as well since they cost 10x as much and would be completely impractical for 99% of GA piston aircraft.