UPDATE JULY 4
All right, so, so far th heading towards the climax of the Archepelo (or watever its called) Saga. Usually this is when someone's past is reveiled. Raleigh has revieled some of his past, but it was barely a horible past. Maybe more will be reveiled at the end, or Camie's might be reveiled also. So each are missing a part in the "requirements* to become a strawhat. Camie has a "dream" to become a great fassion desighner, but she has not have or reveiled a horrible past. Raleigh has reveiled some of a sad past, but he has does not have a "dream". Plus, Raleigh is a former Roger Pirate, a vice-captain for that matter. Raleigh might be too strong to join Luffy's rookie crew. Plus, i don't think Raleigh will pledge is loyalty to another person.
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UPDATE JUNE 20
Now that Ray-san (i cant remeber how his real name is spelt) has appeared he is about equal to Camie for the next Strawhat
Reasons: Almost all of Luffy's crew didn't want to become pirates, but Luffy's persuation got them to be pirates anyway. Ray-san is a former pirate and wants to live a peaceful life. Luffy's persuation could peruade him out of it. Theres been a trend where the next Strawhat has been older than the next. Robin, Franky, Brook, each being older than the last. I'm almost certain Ray-san is a little older than Brook's age (88). His ability "Hak" could not take down The Starwats, Kid, and Law.
Reasons for not: Ray is an experienced pirate. His former bounty is probably higher than the 11 supernovas'. His ability "Hak" could be stronger than the one demonstrated, strong enough to defeat the 11 supernovas.
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UPDATE JUNE 9
Since Hatchan was severely injured i doubt he will join next. I HAVE A HUGE HUGE HUGE FEELING FOR CAMIE NOW!!!!!!
NEW REASON: Luffy always seems to raise his bounty every time he saves a female strawhat. For instance, saving Nami: The marines acknowledged Luffy after him defeating the strongest in the East Blue. Saving Vivi (technically nakama to the Strawhats): bounty was raised after defeating the former Shichibukai Crocodile. Saving Robin: Bounty was raised for starting a war with the World Government, defeating Lucci, and surviving the Buster Call. Now Luffy just punched a Tenryuubito, which will cause him to be a target of the Marine Headquarters and the other Tenryuubito, after Luffy survives this his bounty will be raised. And guess what? Camie has been captured and is currently part of a human auction. Luffy is trying to save her. So my point is Luffy's bounty will raise all for the sake of saving Camie. And Since there's been a tread where Luffy's bounty only raises when he is trying to save a female STRAWHAT, so it's speculated in my mind that Camie will definitely join!!!!!
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UPDATE MAY 1
All right. so Duval has been crossed out, in my mind, for next Strawhat. Hatchan has been lowered and the only person equal to Camie, is the unnamed coating craftsman engineer person guy. regardless on who joins, i'm still paring up Sanji and Camie

Reasons for Hatchan, he can fight, he's a former pirate, his past has been revealed but it's not a horrible past. A horrible past could be revealed though. Abilities: 6 sword style

Reasons for Camie, She has a dream to become the greatest designer, Robin suggested she had a "horrible past" on their current location, unusual people have been joining the Strawhats (a reindeer, a cyborg, and a skeleton) a fishman would not be unusual for there are a lot fishmen pirates, lowering, in my thoughts, the probability of Hatchan. Abilities: can breath underwater, talk to sea creatures , and, being a mermaid, can swim at high speeds.


Reasons for that other guy, He's a former pirate, Abilites: claimed to be 100 time stronger the the 11 Supernovas and The Strawhats