If this were solely a Meta problem, you're right that there are really two logical solutions today:
- It could be done with tags, just as you suggested, or...
- it could be put as a custom OT reason, since that's where things that are site-specific now live.
But as you point out, the problem with the second one is there's already been some concern that "Off-Topic" isn't a totally intuitive name for some site-specific reasons.
And "was totally on topic but is no longer relevant" strains it a lot farther than the other examples we've seen raised. (Side note - that's one of the pieces of feedback we're watching carefully as we roll this out more broadly; if it seems like re-naming those to something else will work better, we'll consider it.)
But I think this idea may be relevant to a broader group of sites
Many of the specific concerns with the loss of "too localized" seem to be circling around questions that might be captured under something like "no longer relevant", as they've been obviated by changes in the outside world, they wound up being about something trivial like a typo that's been found, etc.
Now, we're not going to start tacking on even more new close reasons quite yet. We want to watch and listen for a while first, but we are hearing some pretty reasonable concerns raised. A reason like might address a lot of them, so we're going to see what else we learn from the broader rollout to ensure we have the complete picture, and go from there..
Given that, I'd be reluctant to create a formal status tag now that we'd want to educate folks on, etc, since we know we want to look at this issue for potentially more comprehensive solutions.