Well, sure, have it as an option, but I wouldn`t use it. It seems silly to want to control how another Faction acts in its fights towards another, just because you don`t like it, so you want a never ending war which is even more ridiculous.
The issue is that AI factions are surrendering to other AI factions they are at war with, when 4 or 5 or 6 factions are BETWEEN THEM. They are not losing planets. They are not fighting. They look at relative power and said "we give up" when there is actually zero threat. On top of that, surrendering to a faction doesn't give that faction the goodies. The surrendering faction selects a faction they have good relations with. In my example, I received 10-15 planet empires and dozens, if not hundreds of ships for just having open borders intermittently with the surrendering faction.
Lastly, it isn't really silly to think that a faction would resist to its last planet. We're talking about the potential for genocide of our virtual citizens. Resisting to the last continent would be par for the course against any malevolent invading faction. I can see surrendering to a benevolent faction maybe, pragmatic maybe, malevolent? No.
