For the most part, no, we should not be reopening most of these sorts of questions.
The reason we don't allow questions about unannounced future events is that we aren't a news source. We'd be spectacularly bad at these sorts of questions if we allowed them. No one here is likely to have any knowledge related to these things that is not public. Even if we did, it would be impossible without a legitimate source to provide an acceptable answer. As a result, there are at least two big problems with such questions. One is that most of them will never be answered, or even answerable. That isn't the case once an announcement is made, so it isn't an issue for this class of question.
However, the other problem is that once an announcement is made, the question is essentially immediately obsolete here as soon as it is answerable. The information gets posted on every major anime website, literally overnight. ANN, MAL, Crunchyroll, and even Wikipedia will all have the information readily available for anyone searching for it. We aren't helping anyone find information that they couldn't already get by going to any of these places (as any reasonable person would do). That's still a problem for the question in the OP, and at this point even if we reopened it and answered it I'm not sure it would actually help anyone.
The argument above that we shouldn't reopen the question just because the answer is covered other places does have its flaws. We tend to be pretty lenient towards even relatively low-effort questions here. However, there's another good reason we don't want this sort of question open. It sets a precedent for lots of future questions, almost all of which would need to be closed. In that sense, it's a huge broken window. In the early days of Stack Overflow, many questions not about programming were asked, and some had pretty useful answers even if they were off-topic. However, a lot of them ended up inspiring a large number of copycat questions which were generally of low quality. This is a big part of why SO began more aggressively closing off-topic questions. This is probably a good lesson to take from SO despite the fact that we're a very different community in terms of standards. Keeping the question closed helps to avoid this copycat problem.
So no, there shouldn't be an exception for most of these questions. The only ones that deserve to be reopened are ones that a reasonable person might ask after hearing the announcement. For instance, if someone had asked "Which light novels will the second season of SAO adapt?" before it was announced, that question could be reopened after the announcement. The run-of-them-mill "Will X get an anime?" questions should not be reopened though. To phrase that a bit differently, questions asking about and announcement are allowed, but questions asking for an announcement are not.
As a note, in my opinion, questions of the form "Will X get an anime?" should typically be deleted fast enough to avoid this issue anyway. There's really no reason not to delete the questions in this case. There's nothing the OP can change to make it an allowable question. In addition, for whatever reason questions like this seem to generate a lot of undesirable traffic, since they're arriving here on a broken window. We should be deleting them fairly quickly rather than leaving them closed and undeleted indefinitely.