I think lateral progression will be almost impossible to implement in a game like this without scaring off most of the player base.

However, more roles than Tank/Healer/DPS would be great. Problem is that they did away with those because they can't solo/PVP well and no one wanted to play someone who mainly buffs or debuffs and roles like "puller" are basically dead since groups no longer find a parking spot and sit there for hours pulling mobs as they respawn.

That's what I miss the most. Now, tanks, healers, and dps are roughly interchangeable. Classes are distinct in play style but not in purpose. And the group mechanics are no longer as rich because of it.