For example, when I am writing within an H3 and I want to quickly expand upon a concept inside an H4, I would like a way to both visually and meaningfully (to Obsidian) delineate the end of the H4 section, clarifying that I am back to writing within the H3.
In order to not invent new syntax, Obsidian could have an interpretation of a certain symbol or word as a heading name. So, for the example I described, I could add an H3 heading with the special symbol or word, and Obsidian would recognize it and style the text as if it were part of that H3 that the H4 is within. In the WYSIWYG implementation, perhaps this heading would disappear from view when the line is not being edited.
Sometimes, bulleted lists are just the ticket. But usually I just force myself to be a bit more granular with the sections, thus starting a new H3 in the example described. In cases where I really do not want to start a new H3, I may add an empty line, a divider, then an additional empty line before returning to writing text within the H3.
This may seem like a strange thing to be so picky about. But I make this request now, thinking that I would like to have my notes and Obsidian interpret the text this way with the possible later functionality of having editable transclusion perhaps with an option to toggle off the inclusion of subheadings. In that use case, I would not want the text I am now adding below the dividers to be captured into the subheading and ignored when using said transclusion without subheading inclusion.