To me it's clear that Oda retconned Luffy's DF to a mythical Zooan, but I'm not sure when. It might be earlier than expected.
It's interesting noticing that in every one of Luffy's major battles Oda is starting to hint that Luffy's DF is more than just rubber.
In Dressrosa
	
	
		
		
	
	
		
			
		
		 
	
	
	
		
		
	
	
		
			
		
		 
	
In WCI
	
	
		
		
	
	
		
			
		
		 
	
	
	
		
		
	
	
		
			
		
		 
	
In Wano
	
	
		
		
	
	
		
			
		
		 
	
Kaido's comment was the most perceptive, outright declaring that simple rubber is not enough to do that. Although this is clearly Oda setting up the upcoming transformation.
								It's interesting noticing that in every one of Luffy's major battles Oda is starting to hint that Luffy's DF is more than just rubber.
In Dressrosa
 
	 
	In WCI
 
	In Wano
 
	Kaido's comment was the most perceptive, outright declaring that simple rubber is not enough to do that. Although this is clearly Oda setting up the upcoming transformation.
 
				 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		