There are lot of theories on what luffy's dream is. I think it is definitely tied to what is inscribed on laughtale.
I read long back the theory about luffy , roger and joyboy had same dream to unite the world without travelling across any blue.
It means he has to destroy red line which can create great flood .
Luffy will definitely come back to fishman island and use noah .
It also ties sanji's dream as well to search for All blues.