ok, this is still not proved (just some rumors I heard), but the truth is there will be 2 free slots in Hyper Night (thats according to the newspaper pic), and one of them is for Sayu...she probably wont get rika's slot, as that one is 1) live radio (means you need to be fully concentrated to prevent saying some dangerous things
), and 2) late night (sayu is still not an adult, so she cant work after 10PM)....that means her show will be pre-recorded (as is Miki's dokimiki)
I can understand point #2, if actually japanese law specifies that... but point #1, as I said in another forum: her TV persona and her radio persona (where she can't be seen) would be very diffferent, and also I think it's rude to imply that her mental capacity is somewhat less than average. I have worked as assistant producer on radio shows here in Venezuela, and I can say that if radio executives are giving someone a show, it's because they believe there's an audience for it. And there are as you say two slots: the radio shows ending are ChanChaka Charmy and Country Musume's Happy Night.
@ JTRIX The newspaper article says that the time slot called "Hyper Night", aimed at young people (on weeknights at 11:30),
"will be adding Morning Musume's Michishige Sayumi and singer/song-writer Uemura Kana to it's personalities." I don't know if they will be toghether or they will each cover one of the slots, the article doesn't really tell.