Currently, I don't believe that Elaine is Kumori, but the earlier thread on this topic got me to ask myself some questions. These questions have little or nothing to do with that thread, but I think that asking the right questions, usually the simplest questions, might lead to some insights or lead us to ask other questions which have importance to the overall story, regardless of whether Elaine is Kumori.
First, if E=K how did she meet Cowl? More specifically, when and where did Elaine meet Cowl? If Elaine is Kumori, barring time travel, Elaine/Kumori must have of met Cowl prior to the events in Grave Peril. We know this because in Dead Beat Harry recognized that he had seen Cowl and Kumori working as Bianca's flunkies at the vampire's masquerade party in Grave Peril.
However, that creates a problem that some readers might claim precludes Elaine from being Kumori. After Harry killed Justin DuMorne, Elaine ran away and found sanctuary with the Summer Court, or more specifically with Aurora. Plus, in Summer Knight, Harry told Elaine that he had searched for her. I think he said, "I searched for you in fire and water." So Harry used magical means in an attempt find Elaine, but because she was hiding in the Nevernever Harry's searches were futile. If Elaine was hiding all that time, how could she have met Cowl?
There are a couple of ways around this objection. First, for reasons we currently have no way of knowing about, Elaine might not have been the only wizard spending time with the Summer Court. Elaine could have met Cowl in Summer and fallen under his influence there. It's possible, but I don't think it's likely. The reason I don't think it's likely is an Occam's Razor thing. Unless Jim decides to kill off Kumori and leave her identity a mystery that is never solved, at some point; if E=K, we will get Elaine's backstory and learn how and why she joined forces with Cowl. Having Elaine first meet Cowl in Summer would force Jim to create additional backstory to explain why Cowl was visiting Summer. Unless this reason neatly ties in with events in the larger world, this would make the story more complicated than it needs to be.
The second and more logical way for Elaine to have met Cowl is before she went to Summer. Cowl could hidden Elaine for a few days and either won Elaine over to his cause through persuasion or nemfected her and the implanted personality within Elaine convinced her to work with Cowl. Cowl could have told Elaine that the only way to remain hidden from the White Council was to disappear for a while and suggested the best way to do this was to approach Summer for help. Again, the nemfected agent within Elaine would have agreed with this plan and could have directed Elaine to nemfect Aurora once she was in Summer. In theory, the real Elaine might not even know what she had done. Elaine might have to have been made into a fine thrall for that to happen, but within the rules of the Dresdenverse it's something that's possible.
This leads to another possible objection; but more importantly, to other questions which have greater relevance to the larger story and to Harry specifically. As I stated above, in Summer Knight Harry told Elaine that he had searched for her. So, why didn't Harry find Elaine before she went to Summer? For one thing, we don't know when Harry learned how to do that kind of a magical search. Harry might not have learned how to do such a search until after he moved into Ebenezar's place and by that time it was too late to find Elaine. It's at this point where the questions become really interesting. If prior to his final showdown with Justin, Harry had learned how to do a magical search which could find Elaine in the mortal world, maybe Harry didn't have the time to perform such a search. How much time did Harry have before the Wardens found him? More specifically, exactly how long after Justin's death did the Wardens find Harry and why were they even looking for him or Justin at all? Finally, whose idea was it to send the Wardens out in the first place?
Even if Elaine isn't Kumori, I think these latter questions may be pivotal to finding out who the other traitor is within the White Council. Yes, through some arcane timey-wimey means, the Gatekeeper might have seen something to alert him, but do you really think Jim will use that device a second time? He could, but IMO it's just too convenient, too easy a solution. I think someone within the Council was in communication with Justin and when the former warden failed to make contact, they set out to find the reason why, or they knew about Harry, guessed what happened to Justin and sent the wardens to find Justin knowing they would find Harry.
I am looking forward to the time when we finally get a flashback scene which features Harry's battle with Justin but one that also tells us when and how Harry was captured by the Wardens.