This is planned in the solution for XWIKI-20696 
A sighted user will not read the breadcrumb everytime when landing on a page. We “say” that in the UI by making the breadcrumb font smaller and lighter than the regular content. We “say” this to limited sight users by not putting it into the <main> region.
The background and position of the breadcrumb in the UI serves the same role as making it a <nav> landmark, it “says” something along the lines of:
- this is one unit (and not just a bunch of unrelated anchors)
- this is an important section, keep it in mind, you might need it at some point.