Here are some suggestions, based on the 30 or so minutes I've spent with the engine:
Minigame candidates: Shooting(target practice), Lockpicking, Dice, Blackjack, Fishing;
Visual effect- a dice rolling animation;
Placeholder asssets- don't need to be pretty, some stock silhouette art will suffice;
Randomness(at least the basic 1d6, 2d6 etc.) Right now I can't find a way to add 2d6+20 money.
Hotspot shapes: Triangle, Hexagon (useful for navigation and hex maps among other things)
Some(or all) of these might already be present and I might have missed them completely, but if I missed them, chances are so will other new users, so make sure they have a mention somewhere in the tutorials and the documentation.
Overall a pretty solid project though. Congratulations!