Tiling a decal would be great! I just had a use for it today, tire tracks. Ended up having to make a super long decal and manually tile it in the bitmap options. Tedious. Same for caution tape, I use it all the time on construction machinery. Workaround has been to create a plane, UVW map to the right size and set the proper tiling. Doesn't work well for non-flat objects though.
Aside from tiling a decal, would be great if you could mask it off, use corona slice or even the slice modifier on them. Use case > mask a length of tire tracks where a moving car hasn't been yet and reveal it as the car moves. I tried to create a moving mask with all three options mentioned as well as a corona distance tex but could not get any to work.