Can make it optional in user profile to avoid bloating the page with something users didn’t want.
Making a hover popup with the OP is pretty simple though, took all of 30 minutes for me to make a functional one that reads from existing JSON via AJAX. Mine was a greedy load though, you could do it where it only loads on demand to lessen the impact. Add another hour or so of effort and it should be as passable as anything else.
I’m a big fan of hovering the topic to show OP preview. Lots of times the title looks promising but the content is garbage, or they didn’t bother with a good title but the post content is interesting. In a small forum where you can read every post, it’s not really needed because you’re going to read everything anyway… but head over to the diablo3 forums or somewhere with hundreds of new topics per day. Having a hover preview is very nice there.