GM BLOG The Battle of Crimsonwood Keep

Everyone seems to be missing the very obvious way they could "require" someone from every class - Just make portals that can only be entered by the appropriate class tree like they did with < 30 in GPQ.

Then it doesn't actually matter that what's inside could be solved by more than one class - If only one set of classes can get in it's "their" room.

It's quite clear they have the ability to do this already - Look at the "door of dimensions" you enter for advancement that are class specific.

But they did say Nearly every class, so its probably more likely that it will require specific skills.