It obviously won't break the game. Konami just think that Cyber Dragon is too good to release for FREE. It's highly possible that they would release it as a UR in EX Structure Deck just like Silent Magician
I know it won't break the game at all. I am just joking but that's what Konami possibly thinks at this point.. why else would they leave it out for so long...
At this point, it's not gonna be in a box, definitely a main box UR...