[carry 2663] Add capabilities support to stack/service commands by thaJeztah · Pull Request #2687 · docker/cli · GitHub suggests that cap-add is now available for Docker swarm. The whole " Explanation for complexity" paragraph and it’s implications are therefore probably obsolete. I’ll attempt to test this as soon as I have some time, if someone beats me to it I’d be happy to hear a report 
Cheers!