I like the combination of two of the suggestions ... diagonal feathers and alternating diagonal lines.
I would place the feathers in yellow to red sections - a complete "diamond" and in the setting corners. In the purple/blue/green sections place one or two lines again on the diagonal "diamond". SITD around the whole block. As for the "smashing" (<g>) not sure how wide it is - if it needs to be quilted. If it does ... perhaps diamonds would draw all the 4 large squares together.
Lovely piece!!