The idea reminds me of questing used in Hearthstone/Heroes of the Storm. Where you receive a new quest everyday that gives you gold/whatever. And you can only hold up to 3 different quests. So if you miss a day you can still do the quest the next day. Their quests are usually something along the lines of "play X character 3 times", or "win 3 games", or "play X class 2 times", and stuff! Although those quests are kinda boring, so it'd be nice to have interesting ones that encourage people to play the game different from how they might normally (but not in such a way where it'd encourage people to troll, lol). And of course the quests should be doable by basically everyone. Maybe an example might be having to do a solo map with no tier 4 units, or to play 3 pvp matches, or beat a map within a certain time. Or troll quests like having to build 20 easter eggs in one game, I like the idea of the reward scaling upward, though!