What are the rules for using wallpaper in an open-concept space? Can I apply it to an accent wall – or maybe two, going around a corner?
Wallpaper is a real step up from a paint finish and can truly make a room feel luxurious. As you note, however, placement is key. Typically, ceilings aren't perfectly square to the walls, and wallpaper can draw attention to such an imperfection.
My advice is to make sure you have baseboards and cornice moulding in place so that the wallpaper has a straight edge to start and stop at. This creates a frame for the paper and also makes it easier to match up the pattern where the sheets join. Another effective way to frame wallpaper is to hang it in a fully recessed panel; I especially like this look with a heavily textured paper.
As for how much of an open-concept space to wallpaper, I'm just not a big fan of going around a corner, as the paper tends to wear more heavily along the edge where two walls meet.