So going off what I did in this post: https://www.reddit.com/r/DestinyTheGame/comments/6ozr7q/i_fixed_the_d2_subclass_tree/

I decided to go even further: http://imgur.com/a/6euzM

Being able to choose between the new subclass... AND THE OLD ONE. Because I like Sunsingers, Defenders and Bladedancers; they don't deserve to be forgotten. (I know we got a bit of the Defender back in the Sentinel tree but I feel too few people are really going to use it unless it's its own seperate class again.)

I also have a theory/idea on how as we progress through the storyline on how we pick up these additional powers. When we initially restore our Light we only get the two basic trees that we got because we got our power back from the corrupted shard of the Traveler. But as we progress through the game we find ways to gain new abilites and our options open up. Eventually once we've defeated Ghaul and his Red Legion and free the Traveler, our powers are fully restored, and we gain the full subclass tree. However we'll need to level up more in order to use them and face Ghaul in the raid.

So yeah! There's an idea. Bungie's probably not going to do this because "balance", but hey it's a fun idea they could consider for a future update maybe.