I have long used Ulysses on Apple, a writer’s editor that uses Markdown. On migrating away from Apple I discovered it exports to Textbundle, which can incorporate images by embedding their urls within the text. According to its website:
The TextBundle file format aims to provide a more seamless user experience when exchanging plain text files, like Markdown or Fountain, between sandboxed applications.
We know that Genode is a strong user of sandboxing so this format seems ideal for a native format for text that needs to link to images and other stuff. Almost all the applications (they are listed at page linked above) using this format are for Apple family of OS but if Swift language was on Genode then perhaps some of those could be ported. Non Apple implementations include Keepmark and Zettlr.
I would certainly use a native Sculpt app with this format to retain access to my work from Ulysses. But perhaps there is the opportunity to make deeper use of it in Sculpt, such as for system documentation etc?