Idea for new players: When you play a champ on free rotation and manage an S...
... you should get a discount in the shop for that champion. The free champ rotation soely exists for having people try out champs - but these champions can also be very expensive, especially for new players. That should encourage experiemting with new champions, even if you don't have the necessary IP funds for them.
Maybe one could also make this 2 S ranks, or X games played, or a stacking discount depending on the number of S ranks... I leave fine tuning to others here, but a system like this would surely help to better this game's absolutely horrible new player experience...