Agh, this is such a tough question to answer 
Ai – I highly doubt that she will be graduating soon. Just like a lot of people have been saying about how she has a huge fan base; she and Reina are the backbone of the group. I think that she probably still has around 2 years or more. If she leaves soon then it would be a complete disaster, MM would lose a significant amount of fans. She needs to stay in the group until other members gather more fans. I suppose she could graduate if she really wants to, but it would be a very Miki sort of move. So no graduation for Ai yet.
Risa/Eri – Hmm, now this is where I got stumped. Risa, along with Eri, have steadily been getting more fans, and more screen time which has been very obvious. But the question is, by the time they get the amount of fans that Ai and Reina have, will that be when they’re graduating? It seems like a disaster waiting to strike. It might take another 2-3 years before Risa and Eri’s fanbase becomes the size of Ai’s or Reina’s and by that time they may want to graduate. So should they graduate now? With their growing popularity as GakiKame they could always form a duo together, whether that be singing, radio hosts, show hosts etc. I think it may be a year before they decide graduate. They seem pretty happy at the moment with their current position. Risa is always happy to be in MM since it was her dream and Eri seems happy with the new amount of screen time she’s getting. But another thing with Eri is that she joined to change herself; she’s done that. What does she do now?
Sayu – What are they going to do with Sayu? I don’t get the feeling that she’s going to graduate any time soon. Morning Musume is about the only thing she can do. What would she do after she graduated? There’s no way she could go solo, and I doubt that she’s going to be put into a new group. Maybe she could do something similar to what I mentioned for Risa/Eri. So, no graduation for Sayu. Somehow I get the feeling that if she did graduate, it’s not going to be all by herself.
Reina – The same thing applies to Reina as it does to Ai. No graduation otherwise it will be the end of MM. If Ai graduates then Reina will be the last one to mainly support the group’s fanbase. There’s no way that that’s going to happen. Reina may very well become the leader but that will still be a while away. No graduation for a while.
Koharu – It’s very true that Koharu has the anime solo career going for her, but I still think that she wants to stick around for a bit more. She’s gathering fans for her being in MM instead of anime which will help boost her popularity even more. I think Tsunku and Up-Front want to use this popularity to attract more younger fans to MM. But they may always decide to graduate her 
Aika – There’s no way that she’s graduating, she’s only joined recently.
JunJun/LinLin – I really doubt that they are going to graduate, they (like Aika) are newly added. But they were called “transfer students” so they may be graduated to form another group.
I wonder if there may be the possibility of a 3 person graduation? Of course, this would have to be after more members are added, but I was thinking that Risa, Eri and Sayu may graduate together. I know it’s not very likely, but it’s just a thought. I don’t see Sayu graduating by herself so she may graduate with Eri, but then again I don’t see them really doing anything together afterwards. Maybe seperately but that’s iffy. I think you need the GakiKame duo if they are going to get anywhere. They’re better together than by themselves. So maybe they might all graduate together. I think that when the gokkies and rokkies graduate, that it will be absolutely depressing. 
