I like to check out the Made with Unity section on the Unity website and try out some of the games. Awhile back I tried one called Shop Heroes that ended up on Steam, Facebook, and mobile at the least. It got me thinking that a tutorial on that type of game may be interesting.
Taking it from concept all the way to exploring IAP and balancing them so that they don’t become required to make reasonable progress.
There are a number of other games which do a store/shop simulation but I specifically mentioned Shop Heroes because it seems to be a successful one built with Unity.