At the end of the day, Emet-Selch and the Ascians DID have a point. Venat robbed them of their right to live, and wasn't as morally pure as she loves to champion herself as. Of course, the Ascians aren't any better so naturally we fight them. I'd like to believe that MY Warrior of Light, as I characterize them would easily do an act that allowed them to save both the Ancients and the Sundered. Even if it means she'd never get to return to her OG timeline. The point is, it isn't fair or right to destroy their civilization just because we personally wouldn't want to live there.

Anyway, as for Emet, I'd say that he never had any plans past that hypothetical, for it was never possible for that to come to pass. It simply wasn't in the cards. I'd also posit that not even an Ancient could conceivably hold all the Light. It's not just Aether, its corruptive aether. Also, have we already forgotten that the first Lightwarden was an Ascian? If we were 9/14ths, I'd say there's a good chance an Unsundered would be equally imperiled by the Light.