Seems like the author is slowly re-inventing pass.
You also don’t need to restrict yourself to using just ed.. The author of pass has a vim plugin that disables plaintext temp files, etc in vim. when vim is invoked by pass.
If you use Emacs, just save a a buffer to a file ending in '.gpg and it will ask for a key to encrypt that file with. On subsequent saves it will reuse the same key.
Indeed; one of the best things about pass is that it’s just text files + gpg + git. After this fully sunk in, I started using it for all sort of non-password data which I edit in vim with the gpg plugin.
There’s also an add-on for Firefox to use pass.
And an android app  compatible with pass.
I wonder if :W is a typo… (vs just W).