I would like to see some changes to the shopping system. 
- A option to expand your shop. In my idea it would cost you diamonds to pay to the server itself. The diamonds costs go down for whatever rank you have. Potentially also a 50% off on the store as a special item. These diamonds wouldn't just dissapear. That would make the economy drop. These diamonds would go into a pot that would be re-distributed through voting rewards and mainly donations/rank upgrades bought with real money as a bonus reward. Could also be rewarded through a weekly giveaway. Or even a lottery.

Expanding your shop could mean a better shop location. A bigger plot to build your shop/higher height limit, more sign shops. Or even an advertisement at spawn. Or potentially an extra shop.
You guys would have to make it balanced. Maybe a beta version to try it out. But I trust this team to make it work!
It would be fun and adds some depth to the shopping systems. It is a big update so maybe wait for next season. 
 

The ranks kinda already determine your shop capabilities. Adding more tiers to the shops as well makes it more difficult to upgrade your shop without forcing people to change their shop plots, otherwise each plot will have to be set-up in a way where they CAN be expanded. Imagine the current shopping area, except take each peddler chest and make sure it has the space to become an ancient's plot if needed. There would be a HUGE spawn, and a lot of it would be empty. I just don't believe it can be easily implemented and still look good.