I think it's Ayumi at this point, and I'll tell you why - her genmates are gone and she has no dancing rival anymore inside the group.
I don't think she particularly wants to be Leader, although I feel she'd do an excellent job at it. She's a good senpai, and you can see how much fun she has with the younger members. But I've tried to put myself in her shoes. She's always been passionate about dancing. She and Sayashi were pitted against one another back when Colorful Era was kicking into gear. She's seeing all these other members leaving to pursue their dreams and now her only real dancing rival (Kaga) has peaced out. And it's not like she's going to consider some 16 year old dancing prodigy a rival if one is found in some upcoming audition.
Before, when Sayashi left, she still had all her genmates to work hard with. Now, they're all getting on with their post-MM lives and she's still there. If I were her, I'd be feeling left behind, especially with 2 younger co-gen members having left. Perhaps she and PonPon have made some pact to stick it out as long as they can together, and I know she takes pride in being the only Miyagi prefecture Musume. But at near 26 years old, you know she has to be looking around her and feeling like something is off. I felt the same when I was still in college working on my Bachelor's and all my friends had graduated and were well into their careers, living their best lives.
Covid threw all sorts of wrenches into the cog works, so we know back-to-back grads are going to be likely. With the upcoming single release, I don't expect any kind of graduation announcement until the winter tour starts. My guess is Ishida and Oda for '23, with another audition. I'd briefly thought Nonaka instead of Oda, but they've been giving her more bones lately - in what I assume to be a transition to a more central singing role.
JUICE = JUICE! 
