Conqueror will need a nerf after preseason hits

Simply because the decoupling of stats and rune trees means that those champions that like this keystone + early AD + early tankiness will now be able to get all three without "useless" (comparatively, for the champion in question) attack speed and being limited to either early tankiness or early AD.

In particular, beyond numerical nerfs, I think that this mechanic:

Melee champions refresh the bonus damage duration by triggering combat effects against enemy champions.

will have to be severely restricted some way down the line. Simply because combat effects refers to everything (for instance, is a combat effect), thus negating the windowed nature of the keystone .