I think the quilt is too small for those, it's only 22" x 26", but they're great ideas and it's all getting me thinking. The curved bits in the bottom of the shell are really quite small. You know that rule about don't sew a curved seam smaller than 1"? Well, the centre of this quilt has curved pieces which are 1/2" x 1/4"!
Normally I hate feathers, but I've just looked up spiral feather quilting in Google Image and I'm rather taken by it. Though not for a 1.5" border, of course.