Thanks for the ideas, I like those. You think a single topic for those things is preferable over maybe a new sub-board?
They are all rather broad subjects. There's already an Art category with the 2D and 3D sub-boards, which is a good starting point. As for Playtesting, I think it could use its own sub-board within the Game Development category. Other things like Writing or Music could probably fall under Art as well. Marketing is a finicky topic because it's not development related. Maybe a sub-board for business related subjects?