If by "next GA" you are referring to squishy champions (like ADC and Mages) buying it then it won't be. There is one thing you are forgetting, that you deal 60% less damage when using it and even if the amount of HP you get from it is high, it's not worth wasting the gold and losing out on damage for it. In some cases with mages, they Might want it if they are a mage who stacks HP anyways and have high CDs and use it's active only when their abilities are all on CD to stall for it, but in most cases mages would rather use Zhonyas/Banshees.
ADCs already have GA which is now great for them, and they can't afford to lose out on 60% of their damage and aren't as restricted by CDs like mages are. Also the item gives you 100% current/max HP only when you are close to 3+ enemies and considering most ADCs and mages would only have 1800-2000 HP by level 18 assuming they don't buy any items with HP on it, you would get at most 1800-2000 HP from it while sacrificing 60% of your damage. If you are playing a squishy champion and you are next to 3+ enemies, it won't take 4 seconds for those enemies to still jump on you and kill you within that time.
The item would only be useful for Tanks, and Bruisers and classes like them. Though true damage goes through the damage reduction so anyone with a lot of true damage might still find some uses out of it but it won't be an item that everyone would build.
