It is not a design goal. It was always stated as fact by both Braves and Brookes. They never ever indicated there was even a chance it would not be included unless you count the vague statements in KS about how there are always risks of the project failing. And that's really the crux of it. They never gave any caveats about offline not being baked into the cake. An analogy would be if they announced Friday that the game will not include keyboard and mouse support because it would remove from the experience they want in their game.
It was a design goal, which got considerable risks attached to it. Yes, they thought for long time they could do it. Now they can't.