I don’t know, but I guess the reason why it isn’t done yet is because nobody perceives it as a problem. It would require a repository plugin to install plugins I think. But it all comes down to plugin distribution and deployment. Mostly if you want something outside the default repository you can just upload it to your own install / stack. If a developer provide alternative download ways. Like a github release for example.
Not for Photos specific but F2 seems to fit some of your use cases. https://github.com/ayoisaiah/f2
Even can use Exif fields as variables in the naming scheme. https://github.com/ayoisaiah/f2/wiki/Built-in-variables#3-exif-variables