I'm not sure if this is intended or not, but it's impossible to hit yourself with arrows while flying with the elytra (and without it), they just go through the player; that means you cannot achieve infinite flight like you can on the java edition. Also, I noticed that when being projected upwards by, for example, a TNT cannon, the elytra cannot be deployed whilst going up, only when falling, which I think also breaks elytra launchers.