For T47224 https://phabricator.wikimedia.org/T47224 I've created a new script https://www.wikidata.org/wiki/MediaWiki:Gadget-EditSummary.js that lets you use custom comments for all of your Wikibase actions on a page. If you like it we can make it a real gadget.