Like a shield that grants more armor the more assists you have, or a mage item, and for that matter, why isn't there a stat unique to heals, shields, etc? We know it can be done, there are items that up their strength, so why don't these things exist?
As much as I would like to see an item like this, there are a few problems with the concept. I'll list them out as follows:
Feast or Famine: The amount the item will give will vary depending on how well the game is going; making it pretty inconsistent. Although it encourages snowballing, in higher ELOs it will be less effective since most players would rather get farm and objectives rather than getting kills. But I guess that's a pretty fair way of balancing though.
Gold Restrictions: Supports generally don't get as much gold income as cs'ers. Thus, they are relatively limited to what they can buy early game; usually rushing the 2nd stage support item and Sightstone first. Although bonus shield health is nice, most players would rather invest in other items that may be more reliable in fights: Locket, Redemption, etc.
Toxicity: Anything that adds to healing, shields, etc. can get pretty obnoxious; especially in late game when CDs get really low.
;p
the problem with those types of items, is that they're going to be snowball items by nature
I would love to see an extra stat added exclusively for supports. Sheilds and heals would no longer scale (entirely) off of ap, requiring this extra stat instead. I believe this would help balance the class as a whole.
