Summer and Josh's Pumped Up Traditional may have started this trend several years ago. And we've looked at framing wallpaper as artwork, but for big impact like Summer and Josh's, cover a large area of a wall and frame it with trim moulding. Here are some examples:
The result becomes somewhat architectural in nature, with inset panels of wallpaper as part of a wall instead of artwork hanging on a wall.
Images: Cole & Son, via Alluminaire, Inviting Home, Architectural Digest, House to Home