First/Third person packet/event.

I understand how niche this is, but it would be wonderful if the server was notified when the player switches to a different POV perspective. It would enable developers to decorate the player with display entities by hiding them while the player is in first person, as they would otherwise obstruct the player's view. 

For the elytra, for example, the player's eyes are at their feet. If we place display entities on the player's head or back location the player would see them because their eye location is at their feet. If this feature were implemented, we can hide these entities while the player isn't looking at themselves, as to not obstruct their vision. 

A change like this would allow us to make "proper" wings, backpacks, tails, etc. 

Of course it would be even better if we could have 3d (animated) armor models. Better yet, add a string list property to players representing player model elements rendered on top of the player character. That way we can add many decorations on the player's body without using up armor or item slots. That is quite a lot of work and would involve more entity rendering types for the arms and legs, so an event for POV switching would be a sufficient and much easier solution.