neptronix I'm interested to know what kind of customization you (and the other people who had the same feedback about templates) would like to do that can't be done with CSS but also doesn't require more than HTML.
From my experience, when I need to edit a template, it's because I add a feature. In a "not single page app" (not even sure how to call that anymore lol) the template and the logic are usually separated between frontend and backend. However in Flarum, you will use a Component that will handle both the template and the frontend logic of the feature. It wouldn't make sense to add the component's template to a global HTML template because it woudln't be connected with its logic anymore.
Of course not everybody will think the same but I find that having the template and code together for front-end Components really helps keep things in their own scope. That's of course part of Mithril's design.
Regarding the matter of reordering or moving things around, I've usually found that doing it by editing templates in other software usually completely breaks core features or extensibility with future extensions/plugins in the future. And if it doesn't break anything it often becomes an update nightmare. Flarum has nice helper methods that can be used to add, reorder or remove items from lists without breaking any compatibility.
Also an important thing to keep in mind is that most of Flarum's features are actually extensions (tags, likes, subscriptions, ...). So they wouldn't be part of any global template anyway. All these extensions use the javascript extension API themselves to register their components.
If you want you can still mostly copy-paste a component into an extension and override its whole view method, then edit the JSX template from there. I suppose that would be the Flarum equivalent of copying a Wordpress template into your theme folder. But doing that really isn't necessary because Flarum provides the tool to alter only the exact parts of the template you need to change.
Again I'm interested to know what you're trying to achieve. There probably still are many thing we can improve in Flarum.
