I have considered:
just plain diagonal lines but am not sure about the spacing.
repeated framing or echoing of the inner border (that border doesn't show up in the pics well) I wonder if this will make the quilt pop or just take away for the existing look that I find quite pleasing??
diamonds that would fill the entire outer border similar to one of the pics below, but with more diamonds
Any way I found these pics buy maybe someone has a completely different idea they would be kind enough to share.