my biggest ask would be for custom colour themes? And maybe a one-time paid app to avoid any future ads (if you are thinking of going down that road). An app or a game with ads and no way to pay my way out of them is an instant uninstall.

Someone in another comment mentioned that they do a timed challenge with friends. This would require signup etc. Even though I sometimes do a race against my son I'd probably not sign up/register just to do this. But if it's purely optional then I think there is some merit there and people who are signup happy may take advantage.

I may also like to see perhaps a second (premium) daily challenge. Not unlimited mode because that would just make me gorge on it and get fed up. But two daily challenges instead of 1 might be something to ponder. Maybe even for a small pay? Just don't make it obnoxious with nags and popups etc.