I actually pitched BigBad an idea about a loyalty rewards program. The example I gave him was this:
So in Mortal Kombat X for mobile, everyday you login you get to tap 1 of 10 cards. The cards have various meager rewards like the equivalent of bits and floppies in this game. As you login every day, your reward level increases until you hit level 10. At that point the rewards are much better, say something like GSP Tix or exclusive Digimon. Once you miss a login, your reward level resets.
I thought it was a good idea.