For whatever it's worth, apparently Yoshida commented on this in Famitsu
this week and (while he maintains everyone is entitled to their own interpretation), Emet-Selch's true feelings were a desire to be proven wrong - to see that the Warrior of Light would overcome the "abomination" plan and prove they really can make the impossible possible, really can bring anyone together. Emet-Selch wanted to believe he really was Azem, or at least Azem-
like, and would give him reason to re-evaluate the sundered. Instead, Emet-Selch saw that the Warrior of Light was nothing but another sundered being - unable to contain the aether of the Lightwardens, which any Ancient would have been able to do with ease, and he was "
disappointed from the very bottom of his heart".
Again, I think we're not saying much, if anything, mutually-exclusive here (or at least I'm still not really getting it). We're shining a spotlight on different things to explain different things; I see that. I touched only on the vague "he wanted Azem to return to the fold" / "he wanted to see if goals were truly incompatible" / "he was back-up scheming" while exploring the logic of the schemes within schemes, and you had something much more focused on and specific about the former and what that means to you, but both jibe with what Yoshida's saying here, no? Emet-Selch, despite the schemes within schemes to advance the calamity all other things being equal, was disappointed that the Warrior of Light didn't validate his Azem headcanon, and moreover seemed to take on the most Azem-like silhouette at the same moment he stood resolved to kill him.