Being able to be a Dragon Knight would break the first act entierly. At first, how did the magisters capure you? You are a freaking Dragon. Once you get your collar removed (thats with assuming that the collar prevents you from going into dargon form) you should be able to just fly away (i mean you are a dragon). Then, as Stabbey already mention, playing as a dragon in a top down game with turn based wouldnt be as awesome as it is in Dragon Commander/Ego Draconis. Another issue would be the story (if they didnt change it).
The divine one was killed by a Dragon Knight. After that, Dragon knights were hunted by the Paladins (Those became the Dragon Slayers).
With that in mind you shouldnt find to many Dragon Knights out there anymore.
A new game with dragon and ground combat like Divinity 2 Ego Draconis? Hell yes, i would love to play that.
Building dragon knights into Divinity Original Sin 2? No.
Maybe we will see a skill that has a dragon theme to it.
