I have to wonder about the choice of custom PHP to generate the pages, especially if you are going to start from scratch when the intention is drastic simplicity?
I can understand the rationale of picking PHP many years ago to hand-roll something, but these days there are a lot of excellent static site generators which might be a better choice? E.g. Jekyll is very simple and flexible in my experience, and you can hand-roll some HTML + CSS and get something looking and behaving (e.g. URL structure) how you like very easily. I have had less success with Hugo (in terms of URL structure etc), but I know a lot of people prefer it to Jekyll for its golang-based compile performance.
Am I missing something for the rationale for PHP here?
It would seem that most of the rules here are editorial/design decisions rather than technical restrictions really. I guess perhaps there is the legacy issue of loads of old articles that are written in PHP that would need to be migrated, but that sounds like something that can be trivially automated and would only need to be done once.