ReferenceTooltips is widely used gadget, and across many wikis (44 wikis). It is important to have this functionality integrated within Cite extension so other wikis will be able to enjoy this functionality, and to make the code maintainable across wikis (what if this functionality is broken? enwiki will quickly fix it, but not sure about the small wikis)
Its functionality should be included within Cite (Roll over any inline citation to see reference information, instead of having to jump away from the article text) and give users to it have as a preference
Once this functionality is integrated, it is important to let site admins in the relevant wikis to know about that, so they can deprecate the gadget in favor to a more maintainable built-in functionality.