I never realized the problem with markup until that phrase "light markup". The problem is that it's designed for a human to edit it by hand with a text editor. It's a programmer designing for a programmer, rather than for a user. It's a plumber designing a sink. A mechanic designing a radio. A busboy designing tableware.

What we should have instead of markup, is a WYSIWYG with keyboard shortcuts. Confluence, for example, will convert Markdown into rich text in real time, and has keyboard shortcuts for its other layout/style options. But the point is to edit it in a GUI, see your changes live, and not need to learn a language in order to edit a document. There are so many problems you avoid by giving the user tools to make their life easier. Markup may be one tiny part of that, but it shouldn't be considered the complete solution.