So the winner of "catching Kaido's son" gets the right to challenge an all star huh. I like that concept/idea a lot.
Man, I really hope that it isn't just there for fake hype.
For now it really seems as if the Tobi Roppo rank isn't actually limiting their potential powerlvl. It really seems to be the only non static rank/hierarchial structure we've heard off until now.. This certainly comes off as "potential YC guys who are waiting for a chance to get a promotion"-thing. Additonally Kaido is positive that they are actually up to the challenge. That's what I'd assume atleast, cause otherwise he would make himself a laughing stock in front of Linlin. And they are ex captains aswell. Shit, I've got hope now.
One alternative scenario I can see happening and I'd like myself a lot aswell would be that one (if it doesn't go as planned):
During their mission they come across the strawhats/the alliance and they get respectively beaten by the person who will later on beat the calamity they would have wanted to challenge. This way Oda could kill two birds with one stone.
We, the fans, would get an on panel clash for sure (protagonists at work), while the calamity slayers, so probably Zoro, Sanji and "?", already can show off their stuff and we have a clear picture of how the Tobi Roppo challengers would have fared against their respective calamity. It would be a handy way to deal with that plotline, but a little mugiwara heavy.
And seems like the numbers get shown. Nice one.