I think that Shanks will meet goofy before RHP vs BBP happens.
I think SHP and RHP will meet in Elbaf. Maybe davy back fight.
Then, shp will go to load star to find burn scar dude. And it will turn out that it's Scopper Gaban, protecting the final road poneglyph.
But, CG will already have met up with him and gotten the final poneglyph copy. And CG will challenge the SHP to a Davy Back fight. Buggy will think that since he has Mihawk, he could win against the shp. And its here that Zoro vs Mihawk will happen. Zoro beats Mihawk and the shp get all 4 road poneglyphs.
Then it's the raftel saga. Shp will obviously head straight there. But BBP will either follow them, or BBP will also get all the pone rubbings and using pudding, they will also find out where raftel is and head there too. I think BBP will confront Shanks for the rubbings he has and probably defeat/kill shanks. So BBP also head for raftel.
And the fated fight between the BBP and SHP will take place on the shores of laugh tale. At the foot of the one piece treasure. With BB having defeated/killed Shanks, beaten Garp, and played the most integral part in Ace's capture and subsequent death, goofy will have multiple personal reasons to end BB there.
I also think the Marines will be in raftel by following either of the crews. And they will be lead by Akainu himself.
So it will be a free for all Battle Royale in raftel.
After shp attain the one piece, its time for the final arc. The war against WG.