Luffy vs Kaidou, in part because of Gears 5, was huge. I think we've got a season and change to go before we see fight unfold and conclude, so time will tell how much JJK grows in popularity and mainstream, pop culture mind share.
The modern setting, gorgeous art, directing, stellar cast and strong comedic writing are all part of what gives the series such a strong appeal. I think it could be one of those that does numbers comparable to do the final seasons of Attack on Titan soon, assuming it's not there already.