I do feel like the game has entered a peculiar end stage. I've quite specific treaties with all but two remaining parties and my industry is large enough that I can prosecute war without any real fear of recrimination.
Ideally, at this point, the game would contain a "fine, I surrender" button because I don't think the nature of the game is about to change; my sensors don't indicate that I'm about to be back stabbed, and even if I was I have a few hundred ships generally moving around my rear in simple logistics motions, which can easily move into combat role.
So, I end up with a choice: win by running down those I'm not in treaty with, or turning on my treatied allies. I guess it's not much of a choice and that, I feel, is why the end game has turned so peculiar.