I noticed there was a comment in the draft for background-repeat-direction (i.e. repeat-up, repeat-down, etc). I have found a number of instances where I wanted a background to begin at a particular position, and then only repeat in one direction like repeat-down, instead of tiling both up and down by using the repeat-y, or conversely left and right using the repeat-x.
A background-repeat-direction property in conjunction with the other background properties would be a fantastic addition to control with CSS.