Well, the resulting *.textpack file (here an example from the TextBundle.org site) is then one file where the original Markdown file and the images are embedded/contained.
I think TexBundle/TexPack this would be a fantastic format to write text with images, but as mentioned before, it is not widely used. (Note to myself: In technology often not the best solution succeeds, but something which becomes for other arbitrary reasons popular…")