Is Riot about to give Rengar % Health True Damage?
http://na.leagueoflegends.com/en/news/game-updates/gameplay/road-pre-season-assassin-update
Rengar is the fiercest hunter on Summoner’s Rift, seeking out stronger and more dangerous prey to hone his skills. In game however, Rengar often finds it safer to repeatedly kill his weakest enemies. We like the snowballing hunt mechanic that the Bonetooth Necklace provides, but we want it to incentivize Rengar to seek out increasingly dangerous foes, not that poor Nami again and again (even if cats do love fish).
We've heard wording very similar to that before, when Riot has describes why Fiora has % Health True Damage. They say she has it so she's not afraid to challenge anyone, tank or squishy. Currently, Rengar has no reason to challenge Tanks, and no tools to do so. If they want him to attack more dangerous foes (dangerous to his success) then they're going to need to give him something to take on Tanks.
I could see something similar to Garen's Villian system too, giving % Missing Health True Damage to a changing target, but you're still looking at some form of % Health True Damage.
... please be nice kitty... 