I like all the ideas here and I would like to add some of my own.

When in the crowd it would be nice to have some cheers and boos. Maybe they set them to your action bar while in the arena. This would be great for the combatants to know who is being rooted for.

Also it would be nice for a large display showing the names of the combatants. This way people can find favorite heroes and villains of the arena and gives champions more than just gil as reward but also notoriety. To avoid lore mix ups it could be a large crystal or something that conjurers summons fire or some element from to write the names of the combatants in the sky.