Oda is probably just doing some tributes to old groups prior to Robin (probably picked her as a cutoff due to Saul and most of those groupings disappeared upon joining): Nami and Usopp, the classic M3, East Blue Quintet, X Mark SHs...
The OG Trio is the only one left to be revived... And when was the last time this trio was relevant? IIRC, during the BB meeting... So whoever they will encounter along the way might be as significant as BB to the grand scheme of things or in the storyline at least...