-When the Happiness going bad how about some dwellers start a fight each other so the Overseer need to break the fight and send them to Quarantine Room until they feel regret.Also the room need some skill dweller to talk to them and give some advice or something that will change their mind for not some chaotic.

-Some of weapon we got like rusty,normal, enchance and more..how about Armory Room that can be upgrade and repair by finding some random stuff from wasteland and dwellers bring it back to the vault so.. we can do some crafting and also finding blueprint by accident from wasteland.

-Installing some Trap inside vault for safety vault if the dwellers not preparing guns and outfit

-Wasteland Trader coming at random times selling some stuff like weapon,outfit and crafting tools also with the random items sells.Good for spending Caps.

-Play Room for Children to keep them from wandering around every each room or Library Room for advlt when they come back from wasteland for stoping by.

Well i hope bethesda keep up some new upcoming update for fallout shelter.Thats all from my ideas