I wouldn't mind if it is Steph as Batgirl as long as Cass is an important part of the title. After the way Bruce treated Steph as Robin (basically just using her to needle Tim and then discarding her) and the way Tim has told her not to be in the Spoiler outfit anymore, it would be deliciously ironic that Steph ends up with a cowl.
Misfit on the other hand - just no. I don't think a character with a super-power works as someone with a "Bat" title.