Horizontal progression would be great if they could pull it off. Unfortunately what tends to happen is someone will crunch the numbers on all the gear and find one piece is objectively better than the rest. If SE would bother to give secondary stats some weight rework a abilities to have dmg modifiers based off secondary main stats and whatnot, we could have something here. or better yet give us gear with some more interesting bonuses. cure+10%, increased thundercloud proc, rage of halone combo +3 & riot blade -2. Something to actually think about?

Destiny has an interesting method with exotic gear. the item level is generally slightly lower than the best raid gear available, but it contains some powerful or unique stat bonuses you won't find any other gear and you're only allowed to equip one exotic item at a time. Something like that could be interesting here

Also It may help if they would slow down with how quickly old content is made obsolete. Maybe instead of throwing echo buffs around so hard we just let old content slowly become easier and easier through the power creep of people getting overgeared for it? At the very least it would keep newer players busy longer and maybe even keep up some of that sense of accomplishment that seems to be stomped on whenever they nerf stuff you worked so hard to beat into the ground.