Use case or problem
More restriction for editable region means, for example, the indent of a paragraph in a “quote” or “code” environment is restricted to 4 space or 8 space, unless I choose to edit in the source mode.
This feature is important and helpful for a note taking software. I makes me to focus on the content itself, rather than how to make notes more visually “comfortable” or beautiful. As far as I am concerned, this feature is exactly what makes a note software different from conventional typesetting or editing tools like Word or Notepad, etc. A good example is Typora, which have me no need to concerned about anything other than the content and make me more productive.
Proposed solution
Sorry, I am not a programmer. But I recommend you to refer to Typora, which has the feature memtioned above, but less inter-file functions, which Obsidian do well in.