I'm sceptical if this works out as intended. While it sounds good on paper I could easily imagine the different creation philosophies from all the different forums clashing against each other. That is, if they ever decide to join in the first place. In that regard I can easily see the people from the Roleplay section having a hugh advantage over all the others, because they seem to be the most versed in terms of worldbuilding/character development and I can see game developers being too busy with their own games.
In general I feel inactivity becoming a hugh problem similar to the happenings at the beginning of PCL
Just keep in mind that when the forum is started, a lot of people want to create their own thread, only to later realize, that it's too much effort for what it's worth it, which means that a lot of those threads will die down and chances are that at the end, there's only a handful of threads remaining and only a selected few are going to be regulars at that point (and chances are, most of them are going to be roleplayers). At that point having a complete forum for this might be a little bit too much.
Even if those people would participate in different regions, that would become really boring, because at the end of the day, it's still only those chosen few who try to contribute.