I haven't found anything in the usual markdown, git, wiki suggestions that the tech crowd here gives that works as well. Inline images doesn't do this. Too bad because I really want a self hosted open source solution.
The best other option is a decent pdf editor because you can paste in and annotate and save without collapsing layers.
I am trying pdfxchanger viewer lately with the watermarks for free editing capabilities but might actually buy the license for the editor. This syncs via nextcloud or boox to my tablet but has limitations.
Regardless, it's definitely a realistic feature to have. I'm thinking of it as a block right now, perhaps a file block, that can be resized and annotated freely. Maybe annotations can be mini, floating, moveable and resizable editors. Would that make a big difference for you?