No idea. I mean, I assume Johanna is permanent and we may get content later. While there are a handful of girls who've yet to have content (Beth, Laura, Ms. Turner,Shasha, etc) BoN has been pretty good about including all the girls he's introduced thus far. When Aunt Maggie first showed up I think she got her questline the very next update.
Granted, I do hope BoN addresses the previously existing girls before moving onto Johanna or Maria's co-worker. BoN has addressed new characters before completing content for old ones in the past before... I guess we'll see in whatever 1.7 version has.