All this talk about how the Big Three evolved over this past decade has got me interested, so I went to ComicVine and looked at all of the
group double issue Shonen Jump covers and looked at which 2 to 4 characters were the most prominent, beginning with the first 2010 Issue till now. If I felt conflicted about which characters were the most prominent, I'd take a look at the TOC of the issue to decide. Here's my results:
You can double check here, with this page containing the first 2010 issue.
2010:
Luffy - Naruto - Ichigo (36 - 37)
2011:
Luffy - Naruto - Toriko - Ichigo (5 - 6)
Luffy - Naruto - Toriko (20 - 21)
Luffy - Naruto - Toriko (35 - 36)
2012:
Luffy - Naruto - Toriko (3 - 4)
Luffy - Naruto - Toriko (5 - 6)
Luffy - Naruto - Toriko (21 - 22)
Luffy - Toriko - Naruto (36 - 37)
2013:
Luffy - Naruto - Toriko (6 - 7)
Luffy - Naruto - Toriko (37 - 38)
2014:
Luffy - Naruto - Koro-sensei (4 - 5)
Luffy - Naruto - Kuroko - Toriko (6 - 7)*
Luffy - Naruto - Toriko (36 - 37)
*This was mainly to promote all the ongoing anime. Nisekoi's actually in front, but it was to promote a special chapter that ran that issue.
2015:
Luffy - Toriko (4 - 5)
Luffy - Koro-sensei (6 - 7)
Luffy - Koro-sensei (37 - 38)
2016:
Luffy - Koro-sensei (3 - 4)
Luffy - Koro-sensei - Kankichi (5 - 6)
Luffy - Deku - Hinata (21 - 22)
Luffy - Kankichi (36 - 37)
2017:
Luffy - Hinata - Asta - Deku (2 - 3)
Luffy - Hinata - Asta - Deku (4 - 5)
Luffy - Deku (21 - 22)
Luffy - Hinata - Deku (36 - 37)
2018:
Luffy - Deku - Hinata - Asta (2 - 3)
Luffy - Deku - Hinata (4 - 5)
Luffy - Hinata - Asta - Deku (21 - 22)
Luffy - Deku - Hinata (36 - 37)
2019:
Luffy - Deku - Emma - Hinata (4 - 5)
Luffy - Deku - Emma - Hinata (6 - 7)
Luffy - Deku - Hinata (22 - 23)
Luffy - Deku - Emma - Hinata (36 - 37)
This is what I've got so far. I believe this is accurate for the most part (The order of some placements can be contested) but I think this paints a good picture of what Jump sees, or tries to promote, as a pillar of the magazine. Seeing the progression is quite interesting: 2014 to 2016 really shook up the magazine, permanently altering the status quo from #2 onwards. I think these coming double issues are going to be really interesting: that tweet may very well signal Tanjiro's entrance into this list, likely as early as Issues 6 - 7, knocking Deku down a peg and booting Emma and possibly Hinata off entirely for the rest of Yaiba's run.
God, whenever One Piece ends, though... it's disappearance will be a vacuum echoing throughout the entire magazine.
SIDE NOTE: After looking at all of these covers, I kind of want Naoshi Komi to draw another romance manga that isn't fucking Nisekoi. His girls are honestly really cute.