Especially please don’t tell me to ignore an industry standard only to offer some bespoke solution as an alternative.
RST and Sphinx are "industry standard". Markdown isn't really a standard at all, nobody uses the plain version, everybody uses informal extensions.
I think starting out with Markdown is fine and if it becomes unmanageable, one can still migrate to RST.
Especially please don’t tell me to ignore an industry standard only to offer some bespoke solution as an alternative.