why in the world would you want a custom input on something that is an enum?
It's not a custom input, it's a common use case.
If you have a function "SpawnEnemy" with enum parameter enemy_type (list values: zombie, vampire, troll), how do you spawn a random enemy?
Or let's say there is a function "SetHealthbarColor" with enum parameter color (red, green, blue etc.) You want to call this function and set color to (Player.health<20 ? red : Player.health<50 ? yellow : green).
If expressions are not supported for enum parameters, then you'll have to do this:
If Player.health<20 then Call "SetHealthbarColor", color:red
Else If Player.health<50 then Call "SetHealthbarColor", color:yellow
Else Call "SetHealthbarColor", color:green
Three lines of code instead of one!