The hovercards are a great idea that I think should be standard. The only problem I can see with them is that they cover other links. For example: when I am going through the "see also" section of a page the hovercard for one link often covers all the other links, this makes looking through links very slow. How I would recommend that you fix this is to make the cards turn transparent and un-clickable when you hover your mouse over the card itself. Also what Awesomeshreyo said about summaries is a great idea.
Topic on Talk:Page Previews/Flow
Totally agree with you!
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