Speaking of Kenshuusei, I could only see one non-debuted one that I thought might have a chance at being an ace, that is Saori Onoda. The other vocally capable ones like Ruru aren't conventionally cute enough to be the ace. Sakura has great vocals, yet my impression is that J-wota don't consider her a face of MM despite having tons of lines because they don't think she's cute enough. Saori is the only one I could see making people go like "ermmagrwerrdd she's so cute I'm going to DIEEE". But even that doesn't mean she's suitable for an ace position in H!P's leading ship. I thought Yanagawa and Funaki were adorable and they were put in Country Girls. In general I see a lot of KSS that people hyped a lot as trainees become just ordinary members in groups. Hamachan was supposed to be wildly popular, but she's not standing out in Kobushi to me at all. It's become more difficult to predict things...
Aside from ace material though, KSS always has good potential. Kaede Kaga has been a fav for ages, but I fear time is running out for her.
Ruru obviously has great vocals.
I think if a new girl joins to take Riho's spot, she'll have to be pretty damn awesome. Kind of like how Riho was back then. It's still unbelievable to me, the pressure she went through at her age.
This is actually pretty crazy; I don't think MM has ever had a period when it didn't have an obvious ace. Nacchi -> Maki -> Aichan -> Riho -> ??? Also it's pretty crazy that Maki overtook Nacchi as an ace while Nacchi was still there... That's also pretty unique.
It was a different time though.
EDIT: But also, if you look at the aces that MM has had so far, none of them had a cutesy voice. They all had a sort of low thing going on. If I recall correctly, Saori has a very cutesy voice? So yeah...
EDIT: No, she doesn't!!! At least talking voice
But she looks very different in photos than in video
Whatevs. I'm an old hag, I can't remember everything.