No they most likely won't. At the amount of reduction it would need, it's no longer really a ISD, and so would serve no purpose in the game itself.There is simply no way to make something with the size and firepower of a ISD fit in a game like X-Wing.
They will release ISD in highly reduced scale
I find your lack of faith disturbing.. I heard the same about people saying the falcon will be the biggest ship in x-wing. Well i understand don't want that the game is changing. But many people want capital ships , and ffg will give it to them for hundred of dollars. Revell did that in the early 90' and the size for the transports there is almost the same and the star destroyers there looked still amazing huge but fine for miniatures gaming. Even Lego has star destroyers and the executor. I doesn't matter how lagre the model is. . What cares is the base size. All capital ships will be released, because enough people will buy them. And many for the upgrade cards too.
If you watch the interview on youtube and read the designers reaction in his face , you know they will come. The ISD is the most iconic imperial ship, and it's seen in many upgrade cards. ( for people often see an hint when spying ships in new upgrade cards)