What if there was a (health) regen item that healed based off missing health?
Maybe there's an item I'm forgetting about, but I'm pretty sure most items just give flat health regen. What if instead of flat regen there was an item that healed based on how low your hp was? Higher regen if your hp is lower than a certain percent, and normal regen if your hp is higher than that percent. The exact numbers Riot can decide.