The current story thread of Sanji gaining Conqueror's Haki is actually a Trojan Horse to explain why Usopp's galaxy level Conqueror's Haki has yet to show itself. Gaban says that Sanji is "burdened with painful uncertainty" in the TCB, and "possess a streak of masochistic instability" in the Viz. Well, who is more debilitated by painful uncertainty and, in his case, cowardice than Usopp? Sanji's power up is just the prelude to Usopp's ascension.
