It is clear that at some point in the story, likely the Wano arc, Luffy will either show or achieve Gear 5 or his devil fruit Awakening. But I believe Gear 5 is his devil fruit Awakening. I will explain why.
A user on reddit created a list of subclasses of paramecia devil fruits.
The only two characters that have officially showcased Awakening are Doflamingo and Katakuri. I believe that these two characters fall under the same subclass which is known as a Producer (Although Katakuri has shown traits of being an Enhancer also). This would explain why these two have similar awakenings where they turn their surroundings into their devil fruit. Therefore, for the other subclasses, they will have different awakenings.
I believe Luffy’s Awakening will not involve him changing his surroundings into rubber, but rather he will be able to morph his rubber body into what ever he imagines. I can imagine his hand morphing into a giant hammer or an axe. This will allow for a greater range of attacks. Like Gear 4, he will be able to incorporate his other gears into Gear 5.
I believe Luffy will look similar to Champion Luffy as he would be able to morph his hands and feet into what he wants. Knowing Luffy, it will be something clumsy yet powerful. His hands and feet will be coated in Haki. I believe Luffy will be able to increase the size of his limbs to the size of small island effortlessly since he will have complete mastery over his body. Like Gear 4, Luffy will be able to incorporate all of his other gears into Gear 5(Awakening).
But how will Luffy achieve Gear 5 and will somebody teach him? For Luffy to attain Gear 5 (Awakening), he will first have to master Gear 4.
This Gear 4 form will utilise Armament Haki and Observation Haki to the max potential. But how will Luffy attain Gear 5 in a short amount of time to fight Kaido? Many other theorist have speculated that this man we saw before the timeskip is Scopper Gaban.
It was stated that One Piece is about 70% done. If we follow the trend of Rogers Crewmates that have encountered Luffy in the story, it goes like; Shanks at 0%, Crocus at 25%, Rayleigh at 50% and Scopper Gaban at 75% (likely where the Wano arc will begin).
I believe he will make Luffy go through very rigorous training and help him harness his devil fruit awakening.
*Theory by Son of They