Well, we err on "new news, new thread", to avoid lots of little bits of news getting lost in giant threads. But that's not a policy by any means. We encourage things like if there's a bombshell or big game within a direct, or a Sony conference for example, people create a thread for that thing as well. E.g. Nintendo Labo.
If you want to have a Directs Update thread, welcome to, I would recommend updating the OP with each direct so it's current. Sometimes threads with no OP updates, we re-assign the OP to maintain the topic, so it's a good source of info for people new to the topic or browsing in from elsewhere. That's our general policy on megathreads of all kinds, whether it's for a really popular game like Destiny for example or a TV show like GoT.
There'll always be crossover, we don't tell anyone where to post about certain things, unless it's 2 threads about the exact same thing (e.g. new game, 2 threads, in which case the newer or slightly better one wins or they get merged). People chat about current Nintendo stuff in the Switch thread (regulars have Switch Squad sigs), before that it was Club U, there's still a 3DS thread I post in, etc.
We try to avoid giant sponge topics, we've
eventually closed up some threads like that, e.g. USTV.. a thread about everything Nintendo for example wouldn't work. With the exception of the Chat Room Thread (that gets restarted occasionally) and some other threads (Switch probably counts, PCGT - PC Gamer Thread), that have their own sort of sub-communities and the community feels they are needed.
There's a bit of history. We generally find super giant threads about one monolithic topic hurt the forum because they soak up a lot of discussion and people basically thread one topic like a giant forum and don't go anywhere else, making that content hard to navigate and discover for people like new SONMers.
This doesn't include a Direct thread, which is more about news-specific discussion than a genre or medium for example. So that's OK.
Much more generally, we're positive about people thinking, I want to discuss this thing, I bet there are other people who do too. So just make that thread and see what happens. We don't want anyone worrying about thread creation and nobody needs permission to create a thread. And certainly nobody will get a snide PM or warning or anything like that if they start something, for any reason, even if they just post a joke thread - we're not NeoGAF (RIP In Peace).
