User blog comment:Fintin/New Crewmate or Allies?/@comment-9022101-20140417223912

Historically, the character with the most developed back story joins the crew. In the past, few characters have received this kind of development without joining the crew. The only non-Straw Hats have been Vivi, Jinbe, Sabo, and Shirahoshi. All 4 of these people have played (or will play) extremely important roles in the story. Because there has been a developed flashback focused on Kyros, he is the most likely.I dont think he will join, but he (or one of the other Riku family members) will play an important role in the series like the other 4 I previously mentioned.