I was assuming Mayu was still in Cherrygrove at the moment so would she be with Mio and Spencer some time soon? If Mio's willing to, she could tell Mayu about her crush on Spencer, which might not end pretty with the whole sibling-like relationship between the two already bothering the heck out of Mayu. Mio's welcome to respond in any way to Mayu's disapproval.
Misaki's also free to talk to about Mio's crush but expect some teasing and probably some horrible advice.

For Hiyoko, I'd kinda like Ryouta to meet Madoka (Misaki's Unfezant, as well as starter) because of reasons.