Gonna throw out one final theory before taking a break from reading the manga because these cliff hangers are killing me, man.
So, we now know that Suo and the Red Chanpuru is definitely not within Bofurin territory. In fact, it’s two hours away (I doubt Suo actually did that commute every day since middle school but it makes for a very funny visual), so Sakura and co will most likely have to travel outside of Makochi to get there. With this in mind, that means that they can’t get the whole school involved unlike the Noroshi arc because if everybody went, then who would protect the town? Not only that, but a large group would end up drawing too much attention.
So, what’s more likely to happen is that they’ll send a relatively small group of some of their strongest fighters to infiltrate bankoku-gai. My prediction of who will end up going: Sakura, obviously. That goes without saying. Umemiya, as the leader (and the only person that could convince Takiishi to tag along and keep him in line). Hiragi and Kaji, since Hiragi mentions in one of the previous chapters that this is a “Tamon team problem” and they both probably feel some sense of responsibility for bringing Suo back as his upperclassmen from the same team. With Umemiya and Hiragi out, I think the rest of the four kings will stay behind to look after the town in their place.
Among the first years, I think Momijikawa will definitely be included, since he was stated to be the strongest among the first years and I could see him wanting to tag along as a way to repay Sakura for helping him in his darkest hour (similar to Togame showing up to help Sakura to repay him as well). I think Sugishita has a good 50-50 chance of joining the team.
But if the Red Chanpuru is as dangerous as Endo says they are, and with the more limited numbers they can bring, I don’t think that Nirei will go with them. I expect Sakura to instead ask him to stay behind and lead the class while he’s gone as the only vice captain he has left. I also think that this is why Endo was brought back into the story — to take Nirei’s place as the primary exposition guy for the rest of the arc.
As for whether or not they’ll bring their other allies along, I think there’s a relatively good chance that maybe 1-2 members from each team (Shishitoren, Gravel, and Ropo Ichiza) will offer to come along. Fifty-fifty chance of either Kanji and Suzuri joining or them sending some of their strongest fighters to go in their stead (because they don’t want to leave their respective turfs unattended for too long since nobody really knows how long this mission will last). For Shishitoren, I think the most likely options are Togame and Wanijima. Togame, because he has closer ties to Sakura than Choji and Wanijima because I don’t think Nii-sensei brought him into the story for no reason and this would be a good opportunity for him to get some screen time outside of the mobile game.
Also, I saw some peeps on here propose the possibility of Suo moving in with Sakura once this arc’s over, and yeah. I can totally see that happening.
Umemiya: It’s good to have you back, Suo! Now first thing’s first, we need to find a place for you to stay.
Sakura: He can stay with me.
It’s either that or he moves into the same apartment complex and they become neighbors.