Hovercards provide a quick view on the first sentences of the introduction of an article. This is especially useful for article quality control as the introduction mirrors the article and everyone understands that "something is not right in it" from this first impression. It would be great to have the option to view more inside hovercards, like using 1/4 or 1/2 of the screen for display and have an additional option for smaller font size, for article quality patrolling. There should also be an additional button to add the hovered article to a personal check list, if the user is logged in.
Topic on Talk:Page Previews/Flow
Allowing the user to add articles to watchlists or collections is a great idea! and something we'd love to explore soon.
We wanted to make the hovercards open really quickly, so we had to balance how much content we pulled in, a half or quarter of the screen could cause the hovercards to feel sluggish, we'll keep listening for feedback and try to balance performance with how much text is shown, thanks for the feedback!
It might also be useful to make another tool, based on hovercards, to visually sweep articles, like using a preview on one side of the screen.
You might be interested in m:User talk:Matma Rex/article-map.js (See screenshot there) which I installed like this.
The idea is to split the screen in the middle and, while hovering over article links (inside an article, a category, a catalog, list etc) on the left we get full preview of it on the right. Hovercards have been very helpful as they reveal poor quality articles, even from the first sentence of the article, and this can be extended.