It would be nice, to see, if the article you're hovering on is on your watchlist, and to change that status, for example with a little star or something like that.
Topic on Talk:Page Previews/Flow
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There are even old specification mockups for Hovercard with watch-star... not sure if this was dropped completely? See also en:Wikipedia:Village pump (technical)/Archive 134#Unlabeled star is meaningless to newcomers and many advanced editors
That is actually not a bad idea :-) First I thought: Oh no, more clutter. But this is a way to bring it to the attention of users to watch articles, and watching articles is the engine of Wikipedia! This is more important than the "Last edited by BotXYZ" stuff, which is mostly meaningless information clutter. Caveat: The watchlist star works only for registered users.