I’m specifically pointing out a few cool characters who happen to be female who have more of a chance than the niche **** being talked about, for those that are dead set on wanting a female.
In regards to the characters you mentioned, I can think of a few reasons as to why they're not so actively talked about:
Jill Valentine—she has to compete with her male co-stars (Chris and Leon), both of whom are popular in their own right and are arguably more iconic than she is. There's also the fact that she's part of a company that has a wide pool of franchises with popular newcomer requests, making her uphill battle that much steeper.
Amaterasu—she has the same issue as Jill as she's from a company that has made a lot of popular franchises that have still yet to be represented in Smash with a playable character (Devil May Cry, Ace Attorney, Monster Hunter, and of course Resident Evil).
Dixie Kong—First-party Nintendo character from a series already repped in Smash. I don't know how this DLC cycle will continue to go on, but from the looks of things we're apparently getting only third-party franchises, with the only possibility for first-party characters coming from new games/unrepresented franchise. It seems Dixie's best chance at getting in is in Smash 6's base roster.
I can't say whether KOS-MOS or Reimu would be more likely than either of them because I can't predict Sakurai, but at the very least they don't run the risk of, say, being upstaged by a more popular (male) co-star, or in Reimu's case, compete with other franchises with popular newcomer requests. Some people are wary of getting invested in a character's chances when they know there's steep competition.