Ferocity Keystone or Item passive that grants out of combat Base HP gen equal to ~50% AP(300% cap)
This should scale strictly from AP and be a Keystone in Ferocity tree or be part of an offensive AP item to keep bruisers and tanks form abusing it.
I feel this would basically be the AP equivalent of Warlords Bloodlust.
Since it was impossible to balance an AP Spellvamp Item perhaps out of combat AP scaling sustain could fill the void.
Suggested scaling and cap is just an estimation.
Edit: only problem would be how it interacts with
unique health regen passive.
worth of health regen, and mages typically dont scale as well with base hp gen like tanks and bruisers.
and 6% spell vamp from runes. it's actually better for aoe champions and low damage spammers now.
. It also made volibear, vladimir and mundo op. W/o easy access to grievious wounds any kind of sustain was great.