I think Kobushi and Tsubaki should stay out as they haven't released their major single yet. There are more than enough new faces to the island this year.
Kobushi released a DVD single. It may not be the traditional release but they did release something. Unlike the last few groups which have been going through longer indie phases and then having major debuts, Kobushi is getting one sooner. But the thing is that was when they released singles closer together.