It would be nice if you could select more than one article from a feed to mark them as read or unread all at once.
While I think this would be useful in general, part of the reason I would like this is because I keep clicking the “Updated: X minutes ago” text thinking it will refresh the feed forgetting that it marks the entire feed as read (decidedly NOT what I am trying to do) so I need a way to unread everything quickly.
I would love to have the ability to do this! In fact, what I would really like is the ability to mark as unread in the same way you can mass-mark as read. In the web interface, I can click the cog at the bottom of the UI and select “MARK EVERYTHING AS READ”, then select one day, three days, etc. I would like to have the option to change “READ” to “UNREAD”.
I find that often something will happen and I’ll leave the site and come back and can’t find a particular article and can’t remember what feed it was in. Or just now I managed to somehow mark everything as read (I was cleaning my keyboard, so not really anyone else’s fault 
and would like to make the previous 24 hours’ posts unread again.
Similar features on the iOS apps would be nice, but I find even the mark as read functionality on those devices a little more cumbersome than on the site…