I'd guess that Milf character is going to be the friends mom. Both Milf's Villa and Milf's control had the same best friend+mom added. Then again, none of this matters when even Icstor acknowledges it's not gonna happen any time soon.
I sure as hell hope he won't introduce any more characters, there are already too many that haven't had any/only small amounts of content.
Lets be realistic here, at the current pace (and there are no signs of it getting any better), this game will have 2 updates a year, with progress for maybe 2 characters per update if we are lucky. We currently have, Aunt+Wife, Poolgirl, Judy, Lily, Classmate, Neighbors (and contrary to others, I do like to see more of them), Violett with no or low amounts of content, in addition none of the other characters are finished yet, Celia, Sara, Linda, Caroline.
So we are looking at 11 characters, if I haven't missed any, that aren't finished and going with 2 or even 3 updates a year and 2 characters per update, we are looking at many more years for this game to be finished, so adding even more characters would be disastrous.