The last straw hat before Jinbe was Brook and that was what? 10 years ago? Also Jinbe is already a SH who is very very late, the majority of the story was without him and he manages somewhat since he at least was there as an helper since Marineford pretty much so even if he is a SH now he was promised since the time skip pretty much yet I can't shake this feeling he joined way too late. So, the next SH, according to the pattern we could have him/her in another 10 years? Carrot and every other possible candidates are very weak also we just got Jinbe, the problem is that 10 years from now OP will most likely be finished. So nope, too late in the story, too less time to spend on a new SH to introduce and develop (he will need at least a whole arc focused on him like every other SH bar Jinbe who got some time here and there in multiple arcs) and also the current SH already get too little time in favor of the secondary characters in each arc.