Kuriyama Chiaki. That's who Rena reminds of. Mix her iwth Ayumi and we might have Rena. xD I love her though. That one pic is not the best of hers, but whenever I see her in video and other footage...
I would love her in MM tbh. Also wouldn't mind Yamaga.
Karin I would be okay with and I know she's just 13, but I really would love to see her as a soloist. It would be awesome if there would be some kind of announcement for the summer concert. "kitakore" pretty much sums up what most people would think about it anyway. =P
Starra: Honestly I think Masaki surpasses Eri's goofy, but that'd still make her #2 on that list.