Done. All remaining diy questions are closed; the others have been edited to remove that tag and fix other minor issues. (I also did my best to remove the hardware recommendation aspect when it appeared.) I certainly agree that diy provided no categorization value - it was used on all sorts of things, from hardware improvisation to hardware replacement to novel software setups.
So… I started my own cleanup on diy—including removing the tag from some posts—and then decided, maybe there is a valid reason diy needs to exist? It seems nebulous and many of the posts fall into categories of tutorials or even hardware recommendations that are off topic.