I think the next crew member assuming brooke is going to join will be a merman!!! That would be so cool man
Kinemon (The Samurai)
I think, there are 2 options:
1. merman/maid - yeah, pretty obvious. But, here Oda can get rid of all limits and make something really cool. Or weird.
2. normal human. No crazy design, no akuma no mi. Though stylish and smooth. Someone like an assasin or infiltrator - would be pretty useful in the Impel Down. Of course, ifthere will be such an arc.
Don't worry, be happy
the 9th member has to be a mermaid... Oda put that huge fish tank on the thousand sunny just for the purpose of having a mermaid crew member live in it. I mean what other real purpose would he have put it in the manga other than that one little joke about the shark eating all fish which would leave us with a unmentioned big aquarium that will just faze out of the series forever and I don't see Oda doing that. and I have a feeling it will end up being the first mermaid Luffy meets.
I have a doubt that this next crew would be weird just like chopper, franky, brooke and also robin..not just like before they entered the grand line, luffy just gathered normal humans but has super abilities like zoro, nami, usopp an sanji.
isnt it obvious that brook is joining them?
he's always wanted a musician and saved the best for last.....