Luffy cant eat another fruit or else his body will apart. He'll either put it somewhere safe, throw it to sea or one of the crewmates gets it. Usopp,Nami,Franky,Sanji and Zoro are the only one without DFs but...
-Oda said he wants Usopp to remain the weakest Straw Hat
-Franky having it will contradict his reason for being a robot
-Zoro having it will contradict his reason for being a swordsman
-Sanji already has a thing for fire and he is the best and fastest swimmer so having a DF would destroy his previous development.
The only left is Nami but I just cant see that.