When we look at the Crystal and Weapon build trees, we see two things in common. They both have a burst item (Tension bow, Aftershock), and a stacking item (Breaking point, Dragons eye). Jealth also has a burst item- the Slumbering Husk. But we see on thing missing- a stacking health item.
I feel it would be an amazing idea to add an item that originally has much less health/armor/shield than the other defense items, but after a while of sustaining a teamfight, gives you more health or armor or shield in place. This would really be viable for bruises, and would fit into the theme of the rest of the item trees.
Of course, somethings may have to be adjusted- Rona, Reim, etc. would probably be unkillable, but I feel like thi z would be a unique and fun item to play around with.
*on a side note, I don’t know what the new item would give you, whether it be more health, more armor, or more shield.