Shanks and buggy are currently both emperors going after the one piece. Meaning that their reunion is basically inevitable. Imo they best thing they can do for both their interests is to ally with each other
Ignoring the fact that the red haired pirates are obviously significantly stronger so a fight would not help cross guild at all. Shanks and buggy weren’t just friends but brothers. Buggy at this point would never bow down to shanks and become a subordinate but now that he’s an emperor himself they can team up together on equal terms as allies. Same applies with crocodile and mihawk since neither would probably want to be seen as shanks subordinates either.
Plus cross guild gains way more teaming up with shanks than the other way around. Not only is his crew stronger overall they also have 3/4 poneglyph and get to use shanks ties and connections. On top of that knowing buggy he’s probably gonna plan on backstabbing shanks last minute so he can become the pirate king instead lol.
As for what shanks gains he gets more man power to try and stop Blackbeard with because as his crew is now they don’t seem to have a chance. Like Blackbeard has an admiral in his crew, an impel down warden, level 6 prisoners, and his og crew isn’t nothing to sneeze at either. More so now that they all recently got devil fruit powers
As for when they’d fight with the strawhats? Probably before or after luffy beats Blackbeard
As for potential matchups? I still think a Davy back fight would be really fun but besides that
- Luffy vs shanks because duh
- Zoro vs mihawk because duh
- Sanji vs beckman because 3rd strongest and cool chain smoking ladies men from the north blue. Plus sanji’s initial design had a gun so it’s cool in a meta way
- Usopp vs buggy because both are funny dudes with funny noses that keep accidentally raising to fame. Oda would definitely give usopp an immense bounty too. Also captain vs captain
- Nami or Jinbe vs crocodile because both counter his sand powers. Jinbe because he’s one of the top fighters in their crew and former warlord too. Nami if oda wants to highlight the east blue 5 more and if crocodile turns out to be originally a woman it lowkey helps oda make a woman vs women fight