That’s definitely a cool idea.I've solved some of that by having the magic items grow with the players. As they get more "attuned" the unlock more powers of the magic item
The group has an artificer. I wonder if combining or consuming items could work to make existing items stronger? Like your attunement method.
Im partly hoisted by my own Petard. I’ve combined two magic item heavy APs... Shattered Star and Rise of the Runelords. Im considering not having the shards use up an attunement slot.