I agree with pretty much what locomotion said. His fighting style and appearance are unique which are key characteristics of most of the straw hats. They all have relatively sad back stories too.
Jinbe, like all the crew members, does have a dream which is for there to be friendship between humans and fishmen. However, I'm not sure how him staying on Luffy's ship to help him become Pirate King will help his dream into fruition.
I also feel that Jinbe has no specific place/role in the crew. One could say that he will be the swimmer who will save the devil trái cây users when they fall into the ocean but I don't really see a need for that since it has been shown that Sanji is quite a fast swimmer and Zoro is very able too as well as Usopp and Franky.
Jinbe is also a very able and strong fighter even without being in water and because of this, I feel him being in the crew may break the balance of the 'monster trio' who in my opinion, should always be the strongest in the crew. I feel that Jinbe is equal to Sanji, right now at least.
Although, I'm sure if Oda does make him a straw hat I will accept him into the crew with open arms, right now I don't think he will join. If anything, I think Jinbe will be a stepping stone for Luffy to Big Mom but I guess we will see.
He would shurely complement the crew very well, in terms of appearance as well as fighting style. What makes him different from the other members so far is that every crew member has a function in the crew and a dream to fulfill. In order to make him join, i feel like Oda needs to add these pieces of information first.
I think so, as we already know Jinbe will become the Helmsman of Thousand Sunny and I think the New Monster Trio will be Zoro, Jinbe and Sanji. Luffy will become much different and I think he will become the "Monstrous One".