@publicvoit I just realized from reading the .textbundle/.textpack spec (it's basically a text document with assets grouped in one folder) that the text file's format is not constrained to Markdown per se.
.textpack is basically a zipped bundle, and that would work beautifully with org!
my-self-contained-blog-post.textpack/
- text.org
- assets/
-- image.png
@publicvoit https://textbundle.org/
It's an open convention to, well, bundle assets with plain text files.
Like RTFD includes images in the RTF.
Or rather doc/otf then did, because RTFD never took off outside of classic Mac I think?
But .textbundle is just a directory with a certain directory structure for apps to make sense of and find assets next to the text document.
And .textpack is just a zipped .textbundle.
Christian Tietze
Karl Voit 
Thomas Tempelmann