MONTHLY challenges, with a huge payoff.
Maybe it's a super rare skin, maybe a ton of tokens, or a month of RR+. Be it what it is, monthly challenges could put even the best players on the stand.
Challenges hard enough to be a big feat to complete, but mediocre enough that any given player can complete it with a month's worth of dedication.
I love to have a challenge to look forward to, and I think many could look forward to it. :)