With 1.9 update coming, left click while propelling could toggle on and off elytra's position, allowing the user to pass through 1x1 wall gaps. Just an idea I came up with by looking at the pic.
Good thing that's not what it's meant to be
Actually, If I remember the original post cleary (lazy to get back and read me - don't judge me), it lifts the user one and a half block high, so with collision being in 1.9 you would hardly burn anyone. While the user can ascend higher, which enforces your said problem again, I think that can be solved by not giving it fire damage and/or lift the player more higher as they are floating above the targets head in a few seconds, to keep the flames from burning their head off. It should still deal damage (half an heart), since you're streaming fire, but with my though put into consideration, it prevents well enough for the firebenders to not use this power in means of offense, because fire ski is meant to be a mobile thing.
No, it's not capable of doing such a thing in the way it'll be made. It's not like a rocket stream of fire, you can't just stop in place to burn one person. It shouldn't even have burning effects if I am correct. I could be wrong, I haven't looked at this post in a long time.
It should deal at least some kind of damage or an effect. Fire isn't something you can touch on.
