It's still not implemented, but it's an assumed new feature for when 5.0 comes rolling. I'm talking about the shop update. It'll replace every daily event currency(ranked, survival, arena, group, etc.) and the shops gets a huge overhaul. Moon scrolls/coins are obtainable through the events while the Sun scrolls/coins are obtainable in eventw such as SWB and Matsuri

that's pretty much my understanding.