I agree. Im interested to see what the 3rd subclass for each character will be. Most likely, as you said, it will cover the missing element for each class, as well as a missing role. Hunters, should get a support subclass with void elemental type, titans get a projectile super with the solar elemental type, and warlocks would get a arc elemental super but im not sure of what it would be as they have a ranged super in voidwalker and sunsinger could be considered support with the song of flame perk or even fireborn (self-ressurect) but in my mind its more of a close combat super similar to arc blade or even fist of havoc because your melee and grenade charges fast as heck. So im guessing more of a straight up support style super like the titans bubble. Its fun to speculate and ill be excited when they let us know when and what we will get.