There's two very surprising things that have been aired to the public in Brehon's thread. First, and the main point of discussion within that thread, is that alliances now think it acceptable to refuse a no-punitive-terms peace agreement, and think that they have the right to a white peace on their own terms and at their convenience.
The second, which I'd like to explore briefly here, is that the NPO has offered such a termless peace in the first place. There are two important precedents which they could call upon to easily justify far harsher demands.
The first one is probably most obvious, and regards Fark and FAN. Although Doomhouse got away with one by winning the war in the last outing, pre-emptive attacks by losing alliances could reasonably expect to be treated like TOP and IRON in Bipolar: enormous reparations as a penalty for the aggressive action. Although I've always felt that the terms demanded in Bipolar were unreasonably large, the NPO would certainy be justified in demanding some reparations.
The precedent to go to regarding Sparta comes from the Karma War. In order to protect some of its high NS nations, in that war the NPO sent them into hiding in peace mode and ordered them to stay there, just as Sparta has done in this war. The Karma alliances on that front demanded that NPO bring those nations out to get levelled before they would get peace, and even threatened a reparations escalator for every day they didn't (here is a discussion thread about it). Again, although what happened to NPO during Karma was too much, there is a precedent there that would certainly justify a refusal to give peace until Sparta actually permit the war to be won.
Obviously, to implement any peace terms, NPO would have to get the agreement of its front partners. But I don't think it would find that too hard considering the availability of applicable precedents.
In a way it is a good thing that the NPO is still so frightened of its own Hegemonic reputation that it doesn't dare demand surrender terms, three years later. Karma has actually done its job quite well in some regards. But in my view, alliances which commit aggressive attacks and then lose deserve to have some terms levied.