Could we see a version of Warlord's Bloodlust that was on the PBE this cycle that works for casters?
"You gain a stack of Thirst every second. Critical Strikes and spell casts grant 8 additional stacks over 2 seconds. At 30 stacks, your next attack or spell cast consumes your Thirst and causes you to become Blood Thirsty for 3 seconds. While enthralled, you heal for 100% of your damage dealt up to 25 - 350 health (based on level) that also applies to damage dealt by the triggering attack/spell cast."
To determine the heal cap I took the average AD at level 1 and an average level 18 AD; divided it by the lifesteal value that was on the PBE; and then times by 3... and then rounded the numbers off a little. A healing cap makes it equally strong on single target and AOE mages, which is the major drawback of spell vamp; and 100% healing would feel stronger, in my opinion. It also has the added effect of being less obnoxious on Jhin, Tryndamere and Yasuo, as well as not being pointless on Ashe. :)