Let's keep in mind one of the first things Starlin did when he started writing the original Captain Marvel series was write out Carol Danvers. Or, rather, just ignore her and never use her, despite her being the major supporting character for the first 18 issues. I love Starlin, but I'm not anxious to see his Carol.
That was me. It was in the story that would have been Ms. Marvel v.1 #25—Carol confronts the Hellfire Club, who are affiliated with Mystique for some reason. The story was half-finished when the book was cancelled, and Marvel eventually finished it and printed it in an issue of Marvel Super-Heroes in the early 90s (along with would-have-been issue #24). The open question is how much of the rest of the Dark Phoenix Saga was meant for Carol, or if it was just the Hellfire Club part. (FWIW, the Hellfire Club story makes *much* more sense with Carol, since the Mastermind visions were instead Carol's Seventh Sense visions—Claremont had to bring in Mastermind to keep the vision part of the story when he changed heroines.)
I definitely see this as one of the top possibilities—a short run by Ellis, prob. followed by someone much lower profile (i.e., lower paid) who can continue in his footsteps. Ellis is also the male writer best suited to easing the worries of the fanbase since he's already co-written it with DeConnick.
That said, I'd say we're probably most likely to see Kelly Thompson continue after Secret Wars. I'm not saying it's a sure thing, and I wouldn't be shocked to see someone else writing it, but just that she's probably most likely of the lot.
The second volume got a bit more press, but, yeah, Kelly Sue's first volume got minimal press initially and then was swamped immediately after by all the Marvel Now launches. It was a book set up to fail.
Of course, because of that, Kelly Sue only thought she would get six issues, and managed to get 30-some. I think part of the flailing after the initial arc was her "oh, wait, I have to write more?" period. Like a lot of people, I found the tumor/memory loss the low point of the series, though I liked the revival/use of Yonn-Rog. I just wish she didn't return to the memory loss thing with Carol, who frankly deserves to finally be over the after-effects of Avengers 200 35 years later.