This is legally distinct from my last suggestion I swear.
A lot of games have season quests, like Fortnite. I think they'd be a cool thing to add to CUE.
You'd release some small number (like 2-4) quests every week that would stay active until the end of the season. These quests could be themed towards the season thanks to them being the same for everyone (e.g. "Win x games with a deck containing y "Devil" cards" for the upcoming season). They could have rewards similar to weekly quests, or have more unique rewards. If someone completes every season quest over all 6 weeks, they'd get a special cosmetic or something.