I very much doubt it'll be the next imperial big ship. The Endurance is 1,040 meters long.
I know we won't know until we know. But what do you think about the possibility of an Imperial II-class frigate as a huge ship for the Empire? It's still 400 meters, over twice the length of the CR90. But it's far closer to a realistic size than a Star Destroyer. And it's a pretty cool ship.