Create a time-based tag for content that will, or is now, dated?

Question

I propose a "time-based" tag, which lets people know that the question (& answer, if any) are subject to near-term exportation or staleness. The same would be applied to old questions that are dated and no longer very relevant.

Some questions are timeless.

Other questions address situations that change, such as

1. demographic practices,
2. uses for tools that may come & go,
3. practices governed by laws that have changed.

Such a tag could also be a compromising ground against closing questions that are otherwise valuable. (this topic has come up in other SE.s)

Answer 1

The wiki/editing features of this system allow us to continually improve these posts, so ideally these posts should never go out of date. If the circumstances of a post change, the answers should be updated. And if the question becomes so wrong (or irrelevant) that it no longer serves any useful purpose on the system, it should be closed and removed.

Tagging isn't designed to convey this type of information. Tags are there to tell you what the question is about. Tags are not supposed to be used to add other types of information about the question (like conveying the status or usefulness of the question). In Stack Exchange terms, these are called "meta tags" and are explicitly discouraged.

The Death of Meta Tags

They blog post affirms that we don't 'tag' questions as "wrong", "no longer relevant", or "not useful."