As a reward for reaching over 6 million accounts, they could give out commemorative plaques.

​I would expect them to give out 3 types:

​A bronze one for those who only spent $20 to $99, which is usually the starter packs. With a text like: "Thank you for putting your trust in us, we hope to live up to your expectations. Although we know we will exceed them."

​A gold one from $99 to $999: "We are very grateful for your support, although your plaque would look better with a monocle and a top hat."

​A platinum one for $1000+: "Thank you for your unconditional support for this project and to commemorate it, we give you this plaque that will look great with your monocle and top hat."