I will have to disagree with the idea of just dumping multiple subforums into a "slush pile". I see no point in it, and it seems to serve no actual beneficial purpose.
Firstly, it makes it difficult to find stuff you're looking for. If there are a lot of threads thrown together, it would just be a pain to find anything related to the specific fandom you want.
Secondly, regarding purpose, i don't see it. Because it would clean up the root page? How is a slush pile better then just making them subforums? Subforums take up practically no space whatsoever unless you go looking for them.
Thirdly, about the idea of merging Negima and Love Hina into Ken Akamatsu. This is a bad idea for a simple reason. It's not the name of the series. If i go to a forum to look for Negima fanfiction, I'm going to look for either Negima, or Maho Sensei Negima. I wouldn't look for Ken Akamatsu. Even if we assumed everyone familiar with his works also knew his name well, it wouldn't be what they looked for. This is strengthen further by the fact that all other series are named by their titles, not the makers, so there would be no reason to even think of it.
I would rather that all the forums that are going to move, actually just move. Take the forum and make it an subforum in the appropriate place. Keep all the threads, and the folder-structure. If the Ken Akamatsu thing really gets pushed though, make it damn noticeable just what is under that forum, and don't be surprised, ever, that people can't find those fandoms.
I don't see why this is even considered at all. What is the purpose? What benefit is there to it? I really don't see it.