I totally understand not wanting to add features like that, especially anything that would make it feel pay to win, Dappervolk had a huge difference between the free to play vs the pay to play. It made the already dwindling website worse. But I also wholey agree that the current subscription model is highly lacking.
This might not appeal to everyone, but here's some things I'd like that wouldn't affect other peoples experiences with the game and would entice me to purchase the sub:
More backgrounds instead of day and night forest that only I can see as a supporter, Sakura trees, jungles, oceans.
Extra inventory slots for wolves that isn't purchasable, basically every wolf will just have an extra slot already there.
Wouldn't affect other people's gameplay and people can purchase permanent ones. Plus no one would know if
yours was purchased or not.
Randomly give gifts: A present box that can be sent to one random player per month. (As long as they accept them on their account) Inside could be a random item, or even a random moonstone item. People would only be allowed to receive one monthly too. I love giving people stuff, even if I don't know who that person is. Just making someone's day is nice!
Things I would avoid would be: Anything that is ease of use or for comfort, anything that shows you are a supporter. (It would be a social divider) Anything that gives you major unfair advantages in games.
Things I would want are: Some personal customization that's only visible to me and not to other users, ways to use my support as a way to lift other players up and be more social.