I hope we don't get another YML, an inferior and minute subset of XML's capabilities with all its problems and none of its advantages and tooling. I've used XML for years and once you understand it properly it's fine.
Call me old school but I find lightweight markup to be a hack job.
The best way to think of it is that markdown is a replacement for .txt. It's not a typesetting language, it's just a conventional way to structure text documents.
Most of the elements of markdown are already there in .txt files from the 80s and 90s. All markup does is standardize how to do headers, lists, code blocks and bold/italic so that you can generate documents that actually contain those elements, but could also just treat a markdown file as a normal .txt.
Invariably, if I work on the document for any lengthy period of time, I end up giving up on using Markdown. I'll generate LaTeX output using Pandoc and just start editing it manually.
Ok, you're not going to use it if you need actual typesetting, for that just use TeX and be done with it. What we're seeing I think is the same type of backlash that spawned YAML from XML.
Funny thing is, the actual space for .docx or .odt could be shrinking, is it?