Back to the Molly as Titania suggestion. It makes as much sense as Molly being Mab. If Molly was/is Titania, it explains why Harry has never seen her, because Harry recognizing Molly as Titania could possibly cause a time paradox. It's why Titania didn't kill Harry while he was defenseless at the end of SK after he had killed Auora. Also, Mab knows/knew that Molly had a thing for Harry, so she wanted Harry as Winter Knight out of spite and
broadcast the ceremony throughout winter so Titania/Molly would be sure to see it.
I'm also super glad that the scenario in the second olgaf link didn't happen to Harry, although I'm sure that Toot would have found it interesting.