I've played a number of different games that use different tiers of rewards; so for example you have "universal" rewards for completing an achievement; but those with subscriptions or equivalent (in ELY's case, Donor status) also unlock an exclusive reward for being a donor.
So for example; you could have a reward of a unique cosmetic for completing a challenge that everyone would get for that challenge; however those with donor status also unlock a small cash prize on top of that.
It would incentivize players to donate and also complete challenges. Some games only use this additional reward on milestone challenges or exceptionally difficulty challenges etc.. for example, Fallout 76 has a season system that everyone can work through (but those with a subscription unlock additional rewards as they progress).
Just an idea.
But overall, untradeable useful items / cosmetics would be great to work towards and show off at the very least.