Winning 10 or so games on a champion should give a chance for a chest drop.
Once I got a chest on a champion, I still want to play them. Sure keys are great, but if there are no chests to open, then what use are they? I propose that every 10 or so wins on a champion whom you already got a chest form, will give you a chance at getting another chest. I cant be expected to become a S tier player on every single champion because I and many others do not have every champion unlocked. This way at least I can play my mains while also having a slight, slight chance to still get a chest.