I also really like a combination of 2 and seven - the display name works really well for the popup, and considering that the popup is a kind of a "This is who this user is, do you want to add/follow/ban/whatever them" thing, logically it makes sense for the display name to show there. And combining it with 7 helps with the accessibility issues of the popup.

And even if display names are included across the site, I think it'd definitely be valuable to actually have some styles that make comment pages more useable.