Instead of buffing turrets directly (or maybe in tandem with)
Why not make items or champions that excel at defending or empowering them?
It's pretty surprising to me that there's two items that interact with turrets offensively
but none can provide additional defense to it, and we only have one champion who directly interacts with (living) turrets 
I think it'd be pretty cool to see more of this. It's a very under-explored territory.
ult?
?