What if instead of titans, warlocks, and hunters having 3 subclasses specific to them, any class could choose an element to train in, and choose any abilities from that element?
For example, you could start the game as a titan, choose to train in solar, then unlock firefly grenades, triple jump, Sunsinger for super, do on and so forth.
I feel that leveling in this way things could have been more dynamic, and much more versatile, instead of seeing a character and knowing exactly (within the parameters of that class) what their capabilities were, there would be many more things that could happen, you'd never know when someone might use FoH, nova bomb, etc.
I personally hope they change destiny 2 to run in this way, instead of locking each class to a very limited set of abilities.
Edit: I'm speaking about doing things this way for destiny 2, they would have to put more thought into the possible combinations, but I think this would be a much better class system. It allows for more diversity between classes, and when you see an enemy in pvp throw a grenade you won't immediately know what super they have, it'll add a layer of versatility to your abilities that I think would be a good thing for destiny 2