The taken king released with 3 new subclasses and this utterly changed the way the game felt. However with destiny 2 on the horizon and the game set to continue for many years to come, new ideas are needed to keep the game interesting. There are three big things bungie can add to the game; new locations, new enemy races and new subclasses.
An interesting thought would be to have kinetic damage subclasses. Though kinetic damage is technically not a proper damage type,there are ways to make the idea still viable. The new subclasses would have to be slightly more powerful to make up for the lack of a damage type.
As for ideas for the super, the hunter could be equiped with a spear and grappling hook, the titan with a flame thrower and the warlock could create a black hole which sucks in guardians and bullets. When these supers are activited, the guardian would glow white. Though these ideas aren't completely orginal, they would be quite different from existing supers in the game.
Other possible ideas for supers include an axe for titans, which creates a arc of energy when swung and spear for hunters, which when held create a clone of the guardian which attacks enemies.
