It's time to make Zhonya's active a Summoner Spell (Posted on GD first, but is appropriate here too)
And give it something else. Maybe something like activated burst reduction that scales with AP, but I'll detail that further down.
I'm sure someone could dig up a statement somewhere by Riot where they say "Nothing should be optimal in every situation." in reference to items, champions, summoner spells, masteries, runes, or whatever.
But you know what? Zhonya's is optimal in literally every situation for AP characters. Against heavy AP burst? Zhonya's. Against an AD mid? Zhonya's. Need a lot of AP? Zhonya's. Wanna win that team fight? Well if you don't have Zhonya's they're gonna focus you and you'll die. Does your character have strong passive damage around them as long as they survive? Zhonya's Running out of mana as Swain or Karthus? Zhonya's makes your ult/E cost nothing for the 2.5 seconds it lasts. Vi ult? Zhonya's Zed ult? Zhonya's
It gives armor and AP. And you'd think, sure it's great against AD characters. And yeah, of course it is. Unfortunately it's good no matter what the enemy team comp is. No matter what.
Because it gives 120 AP and has that active, it's the single most powerful item an AP character can build and in most cases there's very little reason to not rush it so you can "outplay" the enemy. There are of course reasons, like going OOM on some characters where you just need the Chalice or you can't farm, but again, very few reasons to not just rush the thing.
So you know what? Here's what I'll propose.
New Summoner Spell: Stasis Cooldown: 240s Renders your champion invulnerable and untargetable for the next 2.5 seconds.
Zhonya's Hourglass New Active: Borrowed Time For 5 seconds all incoming physical damage is reduced by 20% (+1%/25 AP) At the end of the 5 seconds, 50% of the damage blocked by Borrowed Time will affect the player but will not bring them below 1 HP.
Okay. So what we have now is a new summoner spell that is wildly effective on most people but still often situational compared to Heal or Teleport if you want or need those 2 spells for their other utility. We have a way to deal with the constant Zed spam as ANY character in a clutch situation, but it still has a fairly long CD so it doesn't hurt him too much. Fiddlesticks, Morgana, Swain, Karthus, and others no longer have to rush it to make their playstyle viable.
And at the same time, we take Zhonya's Hourglass from a must-have in all situations to an item you build when getting wrecked by AD, like it should be anyway. We also lower its effectiveness on characters other than mages by giving it a stipulation that it scales with AP.
This is also a slight nerf to Fizz to remove some of his most frustrating aspects with ZH.
EVERYBODY WINS ON THIS ONE. Rito pls.