My monitors have a resolution of 1920x1200, which is not an included size with the Next wallpaper.  If I select Next as the wallpaper, the size 1680x1050 is chosen, which either results in black bars all around (if it's centered) or a somewhat fuzzy image (if it's scaled).  In part this is, I believe, a flaw in the image selection algorithm (see #375824), but given that 1920x1200 is a not-uncommon monitor resolution, it would make sense to include a 1920x1200.png with Next.  For what it's worth, it looks like these sizes were included in Breeze 5.3 and 5.4.