I find this feature request difficult to understand.
The erratic rendering of nested square brackets is already being discussed elsewhere.
In order to make something “not intrusive”, I’d choose CSS instead of HTML. It is possible to change the visual design of tags with custom CSS snippets. See this post for an advanced example.
Are you aware, that Obsidian Flavored Markdown explicitly rules out the rendering of Markdown inside HTML:
Obsidian does not support using Markdown formatting or blank lines inside of HTML tags.
This means, whatever you place inside HTML tags like <sup> should be rendered literally.
In my understanding, the examples from Wikipedia all fall in the category of footnotes. They either link to a footnote or explain the need for still missing footnote. Footnotes are supported in Obsidian Flavored Markdown.