MediaWiki's skinning system needs an overhaul. Based on the assumption that a skin is the front-end interface with which a user interacts, we should consolidate a list of all classes involved in this process and categorise them by type - skinning, on-page components, whatever.
From there, a path forward toward coming up with something better may become clearer.
@Isarra is this essentially about CSS classes or PHP classes? Trying to work out how I can make this task actionable. Regarding CSS classes for the purpose of skin rendering I'm trying to reduce reliance on these. With regards to PHP classes, my hope is that skin developers don't need to worry about PHP classes - instead they can make use of hooks and register a skin using the SkinMustache class by a simple edit to skin.json:
"ValidSkinNames": {
"myskin": "Mustache"
},and then live happily in templating land (Mustache and later Vue).
This was probably about the css classes that core etc expect to have defined, which may or may not be defined in the extremely nebulous legacy.css (?) files of the time.
Not really sure what the current situation is.