It's not really a surprise there's not much vocal cry for XS these days. She has plenty of fans, but she's a team character and both teams she's a part of, the Legion and the classic Flash Family, aren't exactly around these days. There IS a ton of outcry for those groups though and so she'll ideally be back with both.
In terms of recent problems, Vixen just needs better writing. Until a moment comes where the iron is hot, having her be on a team is the way to go. She's DC's 2nd or 3rd most popular woman of color, but between how her one-shot sold last year and JLA not really doing anything for her character, I don't think a solo would last right now and one failing would just give DC an excuse not to use her. Of course then the problem becomes 'Where should Vixen go now?' And that is rather tricky. Between the four Justice Leagues, the two Titans teams, the Suicide Squad, the Outlaws, the Outsiders and the eventual Young Justice, Legion and JSA books, DC's already gonna have a lot of teams running around. A shame Beast Boy is stuck with the Titans; I still think there'd be a ton of potential for creativity in a book with a team of Vixen, Animal Man, B'wana Beast, Beast Boy and Maxine Baker.