Something clickable in (like text) or on (like an image) a document that triggers a shortcut e.g., a URL.
Provisionally, maybe select text then trigger a macro that copies it to the clipboard then have KM use the clipboard contents as it does a typed string trigger.
Example use case-
A document like:
Could be make clickable to evoke the commands 
Another related idea would be to have palettes be "attachable" to documents and move with them so a palette of a single icon would attach at the location of the text describing its function. This would be less elegant and seems harder to implement.
Another implementation would be to have assignable locations be triggers. To set the trigger the first click on a document sets the location with some settable amount of padding around it so as not to have to later pinpoint a single pixel. The point set is relative to the document. Of course if the document is changed then everything needs to be reset... Future clicks on that location triggers the macro.
This would break open what a palette could be without the coding overhead the Custom HTML Prompt Action requires.
Harkens back to HyperCard days.
Good thing Peter has gobs of free time, an empty plate, unlimited money, and nothing better to do...