If the SHs go to Elbaf, so Shanks, I guess Luffy tries to fight him.. loses but of course they have no hard feelings and party hard after the fight. That or there is no fight but just the party. Then of course there would be other stuff Luffy has to do in Elbaf (giants, Loki and what not).
If they go to Winner island, then BB, there is for sure a fight with BB. If BB wins, doubt it, he kills whatever he can but since it is Luffy everybody escapes. If Luffy win the BB sonewhat escapes. The 2nd is more likely but Oda will not do it since it dehypes the final villain.
Thinking about Kidd you realize immediately the problem and the whole problem for Kid's pirate career... Wherever he goes if he gets cocky, so acts like he is supposed to act (and has not MC lvl of plot armour) he gets spanked. BB will beat him like he did with Law and in Egghead, even if he has not to face yonkos from the start, he will either way end badly (Saturn or Kizaru, Lucci and Kaku, he could probably make enemies of the Vegapunks too..).
Law in Egghead could potentially do even better than Luffy since he uses his brain, then of course, again, there is the plot power. If he goes to Elbaf, Shanks, he will not fight him be Shanks could want to in order to get the road poneglyphs. But doesn't get destroyed like Kidd but just beaten (cause he will not threat the weak captains under Shanks) with no ever lasting injury, probably.
