To be honest, I'd like to see the Predator keystone changed to something along the lines of:
-Hitting enemy champions with abilities causes your autoattacks to do increased damage (AD scaling).
-Hitting enemy champions with autoattacks causes your abilities to do increased damage (AD scaling).
-Damaging enemy champions refreshes the cooldown on both passive effects, up to a threshold.
-You cannot critically hit while either effect is active.
You're therefore rewarded for weaving autos and abilities together to pound on an enemy champion. I would think, given the nature of bruisers, that the damage bonus would be LOWER, but the trade window would last LONGER. No AP scaling means most tanks won't want it, while locking out critical hits prevents most ADCs from taking it. The major issues would be heavy caster ADCs (MF, Lucian), any tanks that make use of AD (Sion, Poppy), and, of course, assassins, who are probably going to see equal benefit from any rune build for bruisers.
However, if you design the damage around being put out over a longer period of time than assassins are comfortable staying in the danger zone, while keeping the damage low enough that the rune is more of a "sustained damage window" than burst, you can potentially keep even assassins from wanting it.