I think one thread for the 7DRLs is fine. If a game warrants more discussion a new thread can be started in a different forum. ARRP shouldn't be moved to a separate forum - it is often major and important news, and isn't any special challenge.
Releasing any RL is a challenge, especially hitting a deadline, but I guess the ARRP just encourages you to release something. I still think one thread for 7drls may lead to confusion. Having one thread for 50+ game releases will not be beneficial to the community or developers. I like to read about game releases but if I had to troll through pages of info about how good Flend's roguelike is then I will probably miss out on a few gems.
I would still like to propose a challenge category, for 7drls to be entered and discussed separately without flooding the announcements. This would also be a great place for discussion while the competition is running.
The category can also be used for other challenge discussions, or even promote people coming up with their own challenges.
I think this would be a better way of promoting the main Roguelike event that draws attention from the outside world and to attract new readers, with out bombarding them with information overload.