I was wondering could you improve shadows by extended the shadow code to blend samples together? i.e. instread of creating an 8K monchrome shadow texture - you'd create a 1K greyscale map by picking picking "8x" super-sampling from a combo box.
This would blend the binary shadow contributions together to get an approximate penumbra region (especially with shallow angled sunlight) - and leave you with a softer anti-aliased edge. Without taking up as much texture space.
I may have missed some vital thing that would make this fail, or not look too good, but it sounds like a good way to get a nicer looking shadow edge.