None of the old members will be back, Maccoi and Aino already confirmed it at press conference.
Maccoi "all the old members have moved on since their graduation and are doing their own things now, so we will start with all new members"
when you read between the lines what DMM is really saying is "we don't need a bunch of girls that are either retired or in the twilight of their careers"
Aino "to be honest, all the graduating members and a lot of the fans are not happy about this news, I think it is too early to bring Muscats back. Some of the members are pissed to say the least. I hope the girls that come to the auditions are serious about becoming Muscats because we graduating members all treated it like there is no tomorrow and gave it all we had. Honestly, I can't support them at the moment, I will have to see how hard they work, and if they can impress me, then I will give them my support"
So the information my friend got about all new members was accurate. So according to him, the AV girls for new Muscats are all decided already; therefore, the audition is probably only for a few gravure member or is simply used as a advertisement.
Based on the twitter response I see, the majority of the remaining Muscats fans are either disappointed with the announcement or are taking a wait and see approach, which agrees with what Aino said. I think this is a good chance for me to move on and graduate and go back to be a fan of a few graduated Muscats members.