Elbaf: to get the last Road Poneglyph
Lodestar?: as the place where they will set sail to Laftel
Laftel: Know the true history/One Piece
Red Line???: For the final conflict with the WG
I can see them going to Lodestar and there we getting the part of the story that will focus more on Teach and Shanks, pehaps Shanks will be there to recognise Luffy as a Great Pirate, pehaps Teach will get there to try to steal the info on how to get to Laftel from the SH, or even try to follow them to Laftel and fight Luffy there for the One Piece.
This Lodestar place seem to be where the people from AK have put the infos about the Poneglyphs, so even If the SH have already know about the stones, we could get some more background explanation abou the Void Century and the Ancient Kingdom.
I would love if the Elbaf arc was like Skypea, a story outside of the range of the great players in the world, more focused only in the SH, i like others characters, but since the PH this alliance have put so much people around the SH that they have had not much time for themselves, and as the group seems to be growing after Wano, a final Arc for them to get more devolopement inside the crew would be cool and put some more deep in the relations between the members.
I see Elbaf as the only place where something like this could happen, they dont have relations with the WG or the Emperors, seems to be one of the last islands of the NW, are said to be one of the strongest army in the world, as we can see by what BM talk and how the WG try everything to get Giants, pehaps with power to go toe-to-toe with the Emperors and the WG and with this we can get some good fights as they seems to be the only nation in the world that could have warriors that could fight the post-Wano SH.