I still believe the resin will be important.
The bubbles that let people move underwater in Fishman Island and Sabaody are made from resin.
This means that if Luffy can create resin from his skin, he can make bubbles naturally to let him fight underwater.
Hody Jones was teasing how Luffy will be able to fight underwater by himself at EoS by coating himself in resin bubbles.
I believe Imu has a water-based Devil Fruit, either a Logia, or a Mythical Zoan (my guess would be Leviathan), so Luffy gaining this power would be really useful.