The help center's on-topic page is supposed to tell new users what they can and can't ask about, and when we close a question as off-topic it should typically be citing this page rather than any meta discussions. Currently, there's no mention of the fact that unannounced future events are off-topic. There's a strong consensus in favor of this ban, for the essential reason that we're a fan Q&A site rather than a news source.
Questions of this type are actually quite common; enough that JNat proposed a close reason for them (not yet implemented, though we've had a number of questions closed for this reason in the past few months). Currently, when closing these questions, we have to direct users to one of the meta discussions where this policy was established, which is not at all ideal. Meta discussions like this are often hard to read and should never be the primary way of communicating the policy to new users. It also serves as a surprise to those new users who do read the help page and don't see this, only to have their question closed. This happened at https://anime.stackexchange.com/questions/7013/will-there-be-a-third-season-of-sekirei and possibly elsewhere.
In order to better communicate this policy, a line should be added to the help center's off topic list. Something like:
- Questions about unannounced future events with regard to anime or manga production: Will manga X get an anime adaptation?
If this is not clear enough, we should also make a meta faq question addressing the subtleties and link to that from the help center. I don't think this is necessary presently since the policy isn't terribly complicated.