Demon Hunter: Infinite Height In PvP Combat (Patreon)

It requires the level 28 Demon Hunter Talent "Rain From Above". 

Very simple way: Activate the talent and use fel rush after approximately 0.5 seconds (some trial and error practice required). The "vehicle" bar should cancel. This allows the Demon Hunter to get higher than is possible using any other method (approximately the height of the Lumber Mill roof in Arathi Basin).  This is very powerful method when flag capping or escaping from certain death in combat.

Slightly More Complex Method:  Activate talent

Use this freeze macro  /run local t = time() + 10 while time() < t do end, originally developed by TRG_semi on ownedcore. (http://www.ownedcore.com/forums/world-of-warcraft/world-of-warcraft-exploits/525945-useful-freeze-macro.html ).

The freeze macro actually works for all classes and was developed in wod, but has survived through to legion and is particulary useful for the Demon Hunter.  The demon hunter will remain in position when activated at the highest point for the time interval defined above. When the freeze macro concludes the Demon Hunter will be hanging in mid-air, with the vehicle bar having faded.

The Demon Hunter can then glide away (eg to cap flag), or alternatively you can input a one minute time interval to keep the DH in mid-air for one minute.  Rain from above will have reset its cooldown and the DH can keep climbling indefinitely, theoretically out of bounds completely (though this may take some time). 

Note the freeze macro has to be spammed to keep working in combat and there is a danger of crashing if done repeatedly.