These are very similar templates which serve very similar purposes, and based on a quick perusal of their code, all specific functionality can be implemented by #switch
ing on the namespace of the page the template is transcluded onto. Having these implemented as separate templates just complicates usage (e.g. it requires two separate example transclusions be listed for the extension/skin archival request form on Phabricator, meaning the requester has to remove the inappropriate one). I'd do this myself, but have no idea how to handle the translation stuff (I'm also not discounting the possibility that there's some other complication(s) that I'm just not aware of).
Topic on Project:Village Pump
+1. Maybe ask Shirayuki?
Seems reasonable to me as well.
+1
Done in Special:Diff/4279189. I'll wait until my change is marked for translation before actually redirecting Template:Archived skin to Template:Archived extension.
Should {{Archived extension}} be renamed as well? Since it covers skins as well now. (I don't really have any good ideas for a more general name; best I can come up with is "Archived component", but that could cover a lot of stuff besides extensions and skins - which might not be a bad thing necessarily.)
Agree the name is non-ideal, but couldn't think of anything better. Also, the genericism of "Archived component" is bad, because obsolete pages about things other than extensions or skins get tagged with {{historical}} instead.
The existing translations of Template:Archived skin can be migrated. After removing the page from translation, translation memory will be unavailable.