Stupid idea i guess but i thought it would be fun to think about a 4th subclass: Ice.
For example an ice worlock "Frost sage" Charged melee slows targets movement and reload speed by 40% for 5-6 second, Grenade that does AOE damage and slowly eats away at the targets super energy for a few seconds and super allows you to freeze targets within a few feet of you. Any damage taken while target is frozen will shatter them+kill them but they can thaw out in a few seconds or unfreeze if a friendly hits frozen comrades with any solar sources.
It would be super end game 6 years from now but it would be a "pure light" all white light element effects. Some sort of prism thing or somthing maybe even combining parts of the other 3 elements. Would be effective against all elements. Like an upgrade to kenetic or something.