I know you want the editor to be enhanced, but meantime here's a couple of ideas you might want to try.
You might prefer using the Sigil editor, e.g. it displays
#173; in the codeview window for shy etc. If you add Sigil to calibre's open with list for epubs (right click EPUB in book details) you can then give it a shortcut, I use Shift+S,
And/or: In this editor I have the special character set to thus:
The purple blobs draw my attention to the existence of a special character such as an en-dash, em-dash, shy etc.
BR