I've seen a lot of speculation and ideas on the forums as far as the 3rd subclasses and what they'll be and supers and perks and etc.
Well let's look at what we already have!
Titans:
Arc-FoH-Close range
Void-WoD-Support
(Missing:Solar-Long range)
Warlocks:
Solar-Radiance-Support
Void-Nova Bomb-Long range
(Missing:Arc-Close range)
Hunters:
Arc-Arc Blade-Close range
Solar-Golden Gun-Long range
(Missing:Void-Support)
So my theory is that for our third subclass we'll just get whatever we're missing :)