It is clear that at some point in the story Luffy will either show or achieve Gear 5 or his devil fruit Awakening.
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).
*Theory by Son of They