Well, to be honest, at Bianca's party Mavra is being described as sexy, only when harry uses his Sight he can see the corpselike appearance of her (and not that easy even). So, she does amintain a vanity illusion to look pretty. Though this might just apply as well...
I also expect to meet Oberon (if he isn't the Erlking) as a counter to Kringle and I expect to see the other 3 archangels turn up in the books.
Are you sure about that, because I think you are confusing the description of Bianca with Mavra? Mavra was wearing a Hamlet outfit; generally not terribly sexy on a woman, except maybe Greta Garbo in similar type outfit in Queen Christina. Mavra (actually her double) was wearing the same thing in Blood Rites and she didn't look hot then. Even if Harry hadn't seen her with his sight, the visible Mavra was not attractive in any way I can think of.
Sorry to disappoint you, but Jim has said that Oberon is dead. He was involved in a romantic? triangle with Titania and Mab and it didn't end well for him. I don't think this is in a WoJ. I think you have to watch his most recent Q&A's on YouTube to see that comment.