Who was the One-Eyed King after all?
In Ch 86 Takatsuki implies, that Arima was real One-Eyed King (explanation behind the title is glaucoma - Arima was partially blind in one eye). Also, in Ch 89, Tatara also recalls Arima in his memories, and references him as "King". So, it is no doubt, that Arima was real One-Eyed King.

Once title becomes "vacant", Kaneki decides to claim it in the end of Ch 86 (we can suppose, he has full rights for it, since he defeated Arima). I believe, not so many people will question, if he is real One-Eyed King, since only several humans and ghouls were aware of One-Eyed King previous true identity. 

As for now, it is not clear, what purpose Kaneki did this for, but this title for sure has some power and influence in world of TG.