First things first - this rant is in no way intended to criticize Oda's genius. I'm sure he had his reasons for Luffy to announce that he wants to find 10 nakama in the very first chapter of the series. Most probably it was intended to make us speculate about who's likely to join throughout the series - that is until all 10 are gathered, though even then, 10 was somewhat ambiguous - does it include himself? do previous 'nakama' count? can it be more than 10? We don't quite know how exact and precise the statement was, and that's not what this post is about anyway.
One thing, however, is seemingly clear to all of us - there will be at least one more new nakama to join the Straw Hats, and the speculation regarding who it will be is driving me nuts sometimes and is often quite frustrating, to say the least.
Every time a new, interesting (or even minor) character is introduced, there will be at least one person pointing out that this character will DEFINITELY be the next Straw Hat member. Every time an old character is reintroduced or shown after the time skip, it's the same story. Even characters that obviously won't join the crew, like Princess Shirahoshi, seem to gather a whole following of fanboys (and girls) who argue that they will definitely join the crew until the very end - that is, until the Straw Hats say bye to them an leave the island. (Why it was obvious? She's a giant fucking mermaid (who can't even board their ship), plus a princess, plus lacks (at least) one important criterion that all Straw Hats have in common).
I want to take a moment to briefly look at each of the Straw Hat members and point out what makes them special.
Luffy - He's the undisputed protagonist, the captain, and he'll definitely become the Pirate King - 'nuff said.
Zoro - He wants to become the best swordsman in the world - the reason is the promise with Kuina and his own ambitions. Luffy helped him get out of a troublesome situation and they've been nakama since.
Nami - Her dream is to draw a map of the world. She has a sad past (Arlong Pirates, Belle-Mère, village held hostage). Luffy fights to liberate Nami.
Usopp - His dream is to become a brave warrior of the sea, like his dad. He has a sad past (Mom dead, Dad left him). Luffy helps him defend his treasure (the village) against the Black Cat Pirates.
Sanji - His dream is to find the All Blue. He has a tragic incident in his past (almost starved to death) and Luffy helps him defend the Baratie against Don Krieg.
Chopper - He sets out to sea to become a pirate because Dr. Hiluluk (his adoptive father) explained to him how great pirates are, and to be with and experience adventures with his nakama - having found nakama for the first time in his life. Luffy helps him beat up the man who made fun of and killed Dr. Hiluluk.
Robin - Her dream is to find the Rio Poneglyph and unveil the forgotten history. She has a sad past (Ohara, Buster Call, always on the run) and Luffy and the others fight to get her back from the government, returning her will to live.
Franky - His dream is to sail throughout the Grand Line on his dream ship as its shipwright. He has a sad past (Tom's death, feeling guilty). Luffy helps him escape from Enies Lobby along with Robin.
Brook - His dream is to meet with Laboon one more time. He has a sad past (Crew dead, alone for decades). Luffy fights to return his shadow, allowing him to join the SH's and overcome his loneliness.
Now, what do they ALL have in common? A goal, a sad past and they join after the SH's helped them win their battles. Those are also the three criteria that all possible future members have to meet for them to be real Straw Hat nakama material.
This also explains why Vivi was never going to stay with them long-term. She had the sad past, in the sense that Alabasta was in trouble and she also had a fight they could help her with; but she has no dream beyond being with her newly-made nakama. She's not like Robin or Chopper either, for whom having real nakama is something new and part of their dream - she had friends before, still has them, and she had a fine childhood, too. Her 'dream' was always fixing up Alabasta and after that was done, it became maintaining the peace there and taking care of it. She had no reason to go with Luffy, other than enjoying being with the SH's.
Now, while these are criteria that make characters likely, there are also those that make characters unlikely. One of them is - does it make sense? No, seriously. People keep bringing Law up, but the guy has his own pirate crew, with his own unique nakama there, and never in a million years will he join the Straw Hats. Why should he? What would happen to his crew? There's simply no need to. Is he cool and awesome? Of course. But he can be that without being part of this crew - he's still part of the manga, but for some people that doesn't seem to be enough. As for me - I much prefer him in the role of an ally who is a Shichibukai and has a powerful crew of his own, than him becoming a permanent member.
Besides - abilities are also important, and with Chopper, we already have a doctor. Sure, he has more skills than that, and is also smart and all that, but that doesn't make him fit in any more. It's like when people asked for Ace to join way back in the day. That was also completely unlikely, given his admiration for Whitebeard, being his own independent character, and there being no way in the world that he would accept Luffy as his 'captain'.
And now this week I read lots of comments calling for Sabo to join. And Koala, too. Seriously? Those guys are with the Revolutionary army, they have their own agendas, they have their own nakama; why would they? Do they even fulfill the criteria? Sure, Koala used to, for example - but now she obviously doesn't anymore. Other people helped her overcome her trauma, others helped her fight her battles and her dreams we know nothing of, but it's clear they are going to have to do with the Revolutionary Army, since she's in that club already - why would she join the SH's? I won't even begin with Sabo...
Anyway, this became a pretty long rant and all, but the main point was - please use your brains before shouting 's/he is gonna be the next nakama for sure' every time a character is introduced, it's giving me a headache reading that stuff every time. Of coure it's fun to speculate and with Oda, anything can happen. He could even deviate from his patterns - though it's unlikely to say the least; but for most characters that are called 'next nakama' by many, it just makes so much more sense to not join. They are great characters without joining the Straw Hats, and that is something I wish more people would realize.
Now, feel free to rip holes into my 'analysis' (aka rant), and I'd be really happy to see more popular 'next nakama' theories torn apart (Kinemon anyone?) in the comments below!