is it possible to display the excerpt in Polaroid layout for the featured post only? I’m looking for a solution that does this best via filter, since I don’t want to hide the text via CSS for SEO reasons.
It’s not possible via filter at the moment, unfortunately.
You could build two separate lists – one to display a big featured post and another to display the other posts. You’d just need to set the Offset option to 1 so it doesn’t display the featured post.