There are many opinions here that are rather do not follow your idea as-is, but I would like to say do not give up if your project is even dedicated for only your use-case. I believe, you already know the way how you write data is exactly what s-expressions in Lisp/Scheme languages are. I have been working in an editor, which has similar syntax but is really dedicated to create easy A4/letter paper print-outs instead of just typical documents. It is really works nice and if you will come with tooling (editor, components, mixins), very low/gradual learning and good execution you might cut out some market share if you will target specific niche if you already know.
About the syntax and tooling - if you target typical user who already knows Word or Markdown, you should also try out to resemble the "actions" they typically would do. I mean, if I would need to create a list item, I think I will support the hyphens or star notation. They are kind of an idiom of a list item already. The same fact is that you can think out of competing with LaTeX in terms of typesetting, pdf rendering, ease of embedding graphs or being a Jupyter notebook/orgmode competitor in terms of running inlined code (i.e. code block), out-of-the-box layout formatting (report, 2-columns, article) etc. etc.