Due to it's current implementation, Blueprint lacks semantical document structure.

One step forward is T107213.
At time being, there's currently no known implementation of document outlines in graphical browsers or assistive technologies. Document outlines are not the way to go for now, but a clearer organization of headings and their sequence in HTML output would bring at least improvement to search engine indexing.

Therefore I'd propose to aim for:

1. <header class="navbar"><h1>on [homepage] or <h6>on [subpages] [Wiki Title]</h1||6></header>
2. <main><h1 class="firstHeading">firstHeading = Article Title </h1>
   1. Wikitext <h2/>-<h6/>
3. <nav id="side-menu">
   1. <h6>[Wiki Title] in-context links </h6>
   2. <div id="toc"><h6>ToC </h6>...
4. <footer/>

Basically, every heading outside of <main> content (= most important document headings) will at maximum be marked up as <h6/>.