My point is enough of it already exists. Also I pointed out the idea of opening boxes in the dungeon full of unique loot, that too would be RNG. But RNG for cash shop items, no. Or are you going to make the cash shop items from those loot boxes sellable on the auction board for those people who are lucky enough to get multiples of an item they already have bought?
Also you don't need to make it take several weeks. All you need are various rewards of various prices. The more rewards you have, the more you entice collectors to earn all of them. Or you make them quality crafting mats and require x2 or x3 of the materials to make things. There are a lot of rewards you could do for such a system without just tossing random boxes with cash shop prizes in there.
