I really want the mugis to become characters that we don't see that often like Dragon or Shanks (well, not to that extent, but to make them more interesting when we finally see them again.) Like we obviously will have some mugis as the main characters for the arcs, but since the series is becoming less and less "strawhats centric", having some members of the crew missing only to see them later would give them much more anticipation for those moments, instead of the everyday life of them always hanging around.
Since we spent the first (?) half of the series developing them, always being on screen and being in fact the core of the series, it would be great to have this other half of the story to give space to other characters now (supernovas, marines, yonkous, revolutionaries, new factions). We saw how much it impacted the story when Kuma separated them, and we saw how they were in Fishmen Island and Punk Hazard: not that different from when they were separated (but Zoro lost lots of his dorkiness and funny stuff), just much much stronger. So to have some character development for them is much needed and would just make sense (instead of having them the same since day 1 pretty much).
Right now we are anxious to see Sanji and the others, i really want this to don't be just a one-time thing. The series really needs to keep the mugis interesting, and at the same time to show how huge and vast the world is, and these two things should go along well.