Sub forums and their respective sections...
Idol section is good idea, but how we will split hairs as difference between idol and singer/artist is often more or less nonexistent. What is an idol? What is an artist? Photobooks, other promotion photos, age, TV appearances or something completely different? Yes, there are Jpop artists and bands that don't fit that much into idol category as they aren't super produced and often write and compose their stuff... but there is still bands/artists that doesn't produce bubblegum pop but are very close to most features of idol.
I like that random idol sub forum it's nice idea. We could add another for non AKB or H!P idols who do music, but that would add even more useless sub forums. As current userbase seem to be mostly H!P fans here. Lot still follow lot of other artists too.
As an example of forum with massive amount of sub forums could be
Aamukampa(a Finnish military site/forum), but that forum has good reason for that massive amount of those. Normally I don't like that feature as it can make forums hard to read and makes posting something somewhere bit hard or random to determine... sometimes that is still nice if reason for amount of sub forums is good.