I'm presenting what fan told a friend, who told me. I looked into every reference and the coincidences could be just that, coincidences, but boy does it all make me think twice.
All this is assuming that Sanji could have a connection with Vegapunk. At one point the crew calls Sanji a genius. Absolutely nothing or foreshadowing? Yeah I know.
On Thriller Bark Sanji reveals he read the encyclopedia on Devil Fruits, the book Vegapunk created. Yeah so did a few other characters like Teach. I know but keep going.
Sanjis blood type is RH- and if you look that up online there are a lot of conspiracy theories regarding that blood type. Theories about RH- people being smarter than normal people and being descendant of aliens.
Sanjis most famous nick name is Mr Prince and hes fantasized about being Robin or Namis prince riding in to save them. A French writer, Antoine de Saint-Exupéry, wrote a book called The Little Prince. The prince is little blond boy from outer space who lives on a little asteroid which looks a little like Sanji stuck on that rock for 80+ days starving to death. Hmmm
Zeff is said to be modeled after a sailor/cartographer/explorer, Captain James Cook. He commanded HM Bark Endeavour. The NASA Space Shuttle would inherit its name directly from the ship Captain Cook commanded. Nah...
The ship that Sanji worked on before it was attacked by Zeff. The Orbit. That can describe a lot of outer space related things as well as the design of Sanjis eye brows.
Sanjis eyebrows are important enough that he was originally going to be named after them. The name isn't important to this theory but it was Naruto.
SBS Ch 55
Q: Why do Sanjis eyebrows circle up at the ends? Is it a fashion statement? If you ask me, its lame!!
A: Hey!! Sit down, now!! Listen!! All people owe their lives to circling!! The Sun and the Moon and the Earth all go around in circles. What if the circling of the Earth suddenly stopped!! The whole world would be deluged by gigantic waves and there would be a terrible disaster!! So remember that Sanjis eyebrows have that kind of energy!! Repent!! Dismissed!
Joke? I dont know.
R: Oda-chan!! Today is the day for you to answer this!! What about Sanji's left eye?!
O: There it is... again. I get a lot of these. So many, in fact, that I usually just ignored them... all right. I will finally answer one of One Piece's 7 great mysteries, "Sanji's Left Eye"!! Come on out, Sanji!!
S: Hey. You called? What? You want me to show you my left eye?! THAT'S what you called me for? Honestly... fine, fine. You wanna see it? There you go, take a good look. See?
O: WHOAAAAA!!! FOR REAL?!! WOW...!!THE SBS IS OVER!! SEE YOU NEXT TIME!!
Sanji's left eye is finally revealed to the world and suddenly he is Wanted Alive Only. Maybe just a coincidence. Someone who was familiar with Sanji finally got the confirmation they needed and want him back for the connection that even he isn't aware of. Someone like Vegapunk who would be one of these people who may know of Sanji's importance. Only someone of importance within the marines or government would be able to make the call that Sanji should be wanted only alive.
Volume 47, Oda straight up calls Sanji an alien and no one pays it any mind.
I'm on board with everything aside from the Vegapunk connections. Too loose at the moment but everything else is something I'm considering.