Obviously it will never touch One Piece's per-volume though, but that's not a terrible fact, it's just like saying Kimetsu will never get to Batman or Superman's sales. It's a different world and comparing to gods is just depressing lol.
I think KnY's new volume sales will increase or stay the same in 2020 as fans who have bought the whole backlog know it will end reasonably soon and collecting all the volumes is a doable feat. Such is the advantage of easily-collectable-length series.
Also to all Double Taisei fans, I at least look forward to it more than most of the other newbies, but I do hope you realize the series is written really poorly? And it fails to deliver on all the important beats. I just think it's very interesting regardless.