I'm extremely reluctant to limit the possible gains by the attacking realm to the regions originally specified. That significantly increases the incentive on the part of the defending realm to drag out the fight, even if they're losing region after region.
I think it's much healthier overall for the attacker to be required to offer peace after taking those regions, but allowed to take more if the defender refuses to accept their loss.
I am definitely considering a system that would mechanically track the regions specified, and whether there were non-territorial goals, and if the war was entirely about territory, automatically offer peace to the defender upon successful conquest of the last specified region. (And, of course, I already have on my list making all of these aspects of goals mutual, so that the defender has to declare their own intentions, even if those are just "don't lose our own regions, and get them to stop attacking us.") I didn't want to do that at first, because it seemed like it elevated territorial gains over other kinds of goals, but it's certainly true that they're the most common goal & desire in war (and once Hinterlands comes out, it will be much easier to go for them).
