Backstory: I attended MagFest in National Harbor (DC area) over the weekend. I was tagging along with a friend and she created a facebook group for everyone to post their location but nobody was good at keeping it up to date.
The Idea: A mobile app where you can let friends track you at a convention.
Deep Dive: This would be a simple location tracking app but to make it applicable for conventions, you would have to overlay to floor plan of the convention. Larger conventions can vary so you would have to start with larger ones to gain adoption.
Users would sign up and connect with friends. Anyone on your list would be allowed to see your location. You would have to geo fence this so you friends are able to track you all over the place :)
You could build features like chat and sharing images as this gains in popularity.
Validation: My friend was asking about this over the weekend. Your first steps to validate this would be to just build the location portion and test it with friends at a small convention.
Monetization: This consumer app would be hard to monetize, the best bet would be ads. You could also sell event related items that vendors could sponsor.