The issue title is "Support tags in pages" ... and I had been intentionally not doing anything about it for a (bad) reason.
I did not understand what the issue was.
Sure, support tags in pages ... how? What's that supposed to mean? What happens when you tag
a page? Should pages be listed along posts in each tag? How? How does that interact with
TAG_PAGES_ARE_INDEXES which turns each tag into a mini-blog?
Well, it was a bad reason because it could have been fixed by just talking to users. So, I did. And I wrote a minimal viable plugin: tagged_pages
It's far from perfect, it's basically a copy of the tags plugin with some stuff renamed, some deleted and some replaced. But it's a start. And now it can be iterated on.
So, talk to users, I guess.