Hibari thinks that tsuna will be a good opponent, and he was at the same level with dino (before the upgrade ) so I dont think that he believes that tsuna and company are weak. In my opinion it
have to be someone new, maaaaybeee kawahira but I dubt it, even if he is one of the representatives there are other 6 more places to fill, maybe with Fran on one of them.
I also dubt that hibari is going to be an opponent, I think he is either in Reborn's team or not in a team at all. If he is in Reborn's he will show up in a crucial time. Fon is require for a Team, Hibari won't like either option at all. It could easily be someone new, which would be as nice as someone we already know. Longchamp was supposed to be rivals with Tsuna since his debut, but after that chapter, traces of him and his Mafia have barely been noticeable. I completely forgot about him until, luckily, I skimmed through some old chapters and saw him. No solid background on him and no notes of abilities yet. Plus, he and his Mafia could fill in some spaces for Team Fon.
Fran can join other teams because we still dont know who was the person he pointed, it will be a pretty good twist if he didnt choose varia nor kokuyo gang, maybe he pointed a member of the family that fon chose, probably a new character, or maybe hibari (he would chase mukuro in that moment) and if that happens it could mean 2 things, hibari and fran will be in reborn's team and that fran is going to became stronger fisically because if he chased hibari all this time it means that he was beat.