Different green speeds are available for practice rounds only. I believe , along with some other players, it would make skins challenge very interesting to have the option of choosing green speeds for this mode. Also It just might slow some of the hustlers down and make people think and learn other speeds.
I know for a fact, that many players after they have become legend or better, tend to forget their speed on the green other than their default tier speed. Seems like this would not be difficult to plug in and not have to create from new.