Big 3 are currently One Piece, Attack on Titan, and Seven Deadly Sins.
I remember someone making this claim on another forum I frequent back when the manga came out last year. I don't read it, so I can't speak for its appeal, but I also don't recall seeing it show up on the manga charts that often. I'm pretty sure it's not even in top 30 for 2015...unless it goes by another name I'm not aware of.
If it gets an anime adaptation though, I can see it getting a boost, as a lot of manga tend to. Would give it a chance at growing in the west too, since anime tend to be more popular than manga over here. No idea if it'll "replace" Naruto, but if the anime is well done I can only see it helping the franchise.
NNID: Zephyr25 / PSN: Zephyr--25 / Switch: SW-4450-3680-7334
