It is a reportable offense categorised as “spamming.”
And yes, this is one of the things that has been explicitly stated.
Doesn’t matter whether one thinks it should or shouldn’t be bannable, because it is reportable, after which it is up to Blizzard to decide what to do. But it is a genuine offense to necro old threads on these forums.
If people want to bring up a really old topic, they make a new post about it. Not necro or ‘bump’ old posts.