They have to re-organize the senbatsu, and announce a new center of course. There's no point in keeping Techi as a ghost center if she's not in the group anymore. And also we have a senbatsu member in hiatus. So with two available spots, I think they should add Riko and Ten so all the 2nd gen can finally be n senbatsu. I only consider those two because I'm fearing more graduations, TBH.