A Star Destroyer and a Death Star will enter this game in some fashion.
As a backdrop of some sort, perhaps. But I don't really think most people will be happy with that.
It's a game, they can ignore a description from the book and make a balanced ship that fits the idea of the ship.
If you mean a new ship that's balanced and fits with in the game? Sure, but it won't be a ISD. There is no way to make a ISD fit in this game. It's simply too large and powerful to ever work in a game scaled for individual fighters.
Even in the Epic Rules, from what little we know, they're not really changing the basic scale of the game, it's still 1 model = 1 fighter.