Nowhere did I advocate for hiding or showing markup. I was very specific about simply the header level. Unless you think denoting the header level in a clear form like H1 automatically makes it markup. In which case, I have news for you.
You must be referring to iOS as the Mac already displays the heading indicator in the gutter. But showing the indicator in the iOS gutter too would probably mean the margin would have to increase, and I don’t really like that idea. B1 has way too big margins for the narrow phones of today, imo.