Before we get a keystone to address bruisers added, we need to have a concept of what a bruiser needs/synergizes with.
All you Jax players out there, what's your idea for a keystone that Jax benefits from more than any existing rune?
Challenge mode: keep your keystone idea from being op/exploitable by other classes.
What would work on a variety of bruisers? Is there something out there that would help Jax, Irelia, AND darius? Renekton?
How about a minor rune to start with: Inspiration rune that grants an item to start the game with. This item is melee only, and provides an active AA reset, but has extremely limited stats. Builds into titanic.