^ I think arian does not say it because of the Gold Era power but because MoMu really needs someone who believes in the group. Now Yossie will be gone, it's like a full circle. Now there's truly no piece from that Gold Era puzzle. So whoever takes the rides must be genki and optimistic about the future, and despite Miki has the skills, she might not have the enthusiasm. I think that's arian point.
We've seen a very lazy Miki in many perfs, and those who lived her entrance to the group will remember her face was not too happy on the first days. She was rejected at first, then made it to solo, then put in the group. Be Miki for a second: would you like this resumé? She's more adult and mature, and she loves Aya, and Aya is in GAM. So either Aya joins MoMu (which my most extended fear since Tsunku added Miki) or Miki just develops a true love for the group and makes everyone show a strength power. Why KAT-TUN sells better than NewS? Because KAT-TUN is the hard-looking rockish boys while NewS are the soft ones, MoMu alike. So if Miki can give MoMu a new "strengthful" image I am sure they will really show a new group.