I've noticed a couple of times now that when a game has a major announcement, such as TSW or Tera going f2p, that mods close a thread related to said announcement, stipulating that it should have been posted in the megathread. Truth be told, I expect that only a core of people follow those threads religiously. Certainly in my case, if such announcements were confined purely to the megathread, I would never have known about said news. I expect there are snippets I have missed in the past also.
I think it's a good idea to let major announcements like this be posted in new threads, so that passers by can be made aware of things they would miss if they were confined to a larger thread that they may be intimidated to start to read, or at that period of time does not have much interest in diving into a thread to see what information might be available.
Obviously rules would need to be enforced to not devalue a megathread entirely. Something like, big announcements are acceptable as a separate thread, linking to the megathread itself in the first post. Allowing only chat about that announcement would keep it afloat for a little time, but it would eventually die off leaving the megathread where it needs to be. Or something similar.