Redneck Parrotheads:the category can be narrowed to only consider Artistic in-service post boxes... like R2D2. I'm sure there's more out there. There's something along this vein that could work if it was written right.
I believe by doing that you'll lose the usefulness of the category. Also, the only really unique ones I have seen are the R2-D2 boxes, and there are several already waymarked in All Things Star Wars. There could be other unique ones, but I'm not aware of any.