Meta could use a close flag of type "no longer relevant".
Examples where this would be appropriate:
- Should we merge the [import] tag into the [data-import] tag?
- Community Promotion Ads - 2012
- What should be our domain name?
- 2013 Moderator Election Q&A - Question Collection
The current practice of using
duplicate for this purpose is a kludge (and in the case of the merge tags example, there is no dupe to point to).