Vivi’s position in the crew is Dancer, that could explain the peacock slashers weapon that she has. Peacocks are known for dancing. Vivi will become a physical attacker because of her dancing abilities. Her hair is literally blue, unlike Franky’s being light blue, so that’s the difference maybe Oda is making here. The difference between her and the other girls in the crew is that her main hairstyle might end up just being the pony-tail, so to differentiate Robin and Nami, Robin will have really short hair (which seems to be the plan).
I think Nami is going to eat the Paw-Paw fruit, however Nami will stop using lightning. She’s obviously going to lose Zeus. Paw fruit works for Nami because it helps with navigation, and she could still use a staff like she always has, she’d just still be in the weak group. Robin might become the strongest girl in the crew, so Vivi can safely be in the middle or vice versa.
Loki is a potential member because he uses a hammer which is a unique weapon. He also has purple hair. In the crew’s early concept art one of the characters had a hammer so he might’ve always planned that and Loki has a dream. The rumble rumble fruit(eneru’s df), will be eaten by one of the members, so Loki eating it would be fitting, although it can go to another member (because Luffy’s is now a mythical zoan). If that’s not Loki’s DF, then whoever will use a hammer as their main weapon in the crew could be Franky (makes sense since he’s a builder). I like how Scopper Gaban always wears glasses because that’s a unique design. Also the crew is missing a member that represents brown, so Gaban’s last namr Scopper is perfect. The person that eats the rumble rumble fruit can either be Zoro or Gaban.