I’m guessing the next arc is a clash for the final Road Poneglyph. Maybe Lodestar or some other final island before Raftel next.
It’s either a case where the BBP and RHP clash first before the Strawhats show up, or it may be an all Yonko simultaneous showdown.
I believe the SHP and BBP final fight will be at Raftel, so I’m leaning towards the first option.