A skill tree similar to AC: Origins would make for an AMAZING character build. Choose HOW you upgrade, the route you take, but inevitably be able to unlock ALL skills. Have a simple toggle to choose class, grenade, melee, rift type...upon further "rank ups" give that bright engram and a boost token for whatever stat you choose, up to X times max.
Also...we got to see cutscenes of various guardians using blended skills. Aren't we to the point with our guardians yet that we are disciplined enough to throw a solar grenade and cast a Nova bomb without changing class? Can't we choose to drop a bubble shield and electro-smack a dreg into oblivion, because that's the discipline and skill route I chose to go? Allow us to see those challenges and let us configure our skills to the challenge. Don't make us step out of the fight to get into a menu to change this weapons element, switch classes, and change to "the other grenade" because this enemies shields and that damage modifiers element.
I would love if we got a skill tree similar to that of Borderlands games. It would be awesome if we could customize our characters really differently from other characters of the same class and light attunement (void, arc, solar).