Riot is planning to hit Conqueror Rune domination with upcoming patch 8.14, according to lead designer Meddler comment on the official forums.
Although this is a relatively vague answer, Meddler’s reasoning for a Conqueror nerf is that it has some anti-synergy with Black Cleaver. His answer was a response to another comment from a player, which cited anti-synergy between the Cleaver and Conqueror as an issue. Both are designed for bruisers to melt through tanks, but they don’t help one another at all, according to the comment.
While that player is mostly correct, a flat nerf to Conqueror wouldn’t actually help that problem. If Riot’s planned nerf were to help that specific issue, it wouldn’t really be a simple nerf at all. It would have to be a bit more complex and would require a change to the mechanics of the rune itself. Otherwise, the anti-synergy will still be there, but Conqueror will just be weaker, and that’s why Meddler’s comment is a bit obscure.
He did say, however, that he feels Conqueror is just outright too dominant, and that’s something we can agree with. It has taken over the game for a multitude of different champion types, not just bruisers who need a tool to counter tanks. Whether you’re playing Master Yi, Miss Fortune, Riven, Darius, Draven, Renekton, or one of the other many champions who have found a home with Conqueror, it’s just way too useful when compared to the game’s other Keystone runes.
These changes should arrive with upcoming patch 8.14 in two weeks.