I agree that longarming is probably not the way to go, but tying it seems like it wouldn't be as stable (and with those fabrics, it might be important). If you could hand-quilt about a quarter inch away from the feather stitching, it seems like it wouldn't take away from the feather stitching at all (especially if you were careful with color choice for the quilting thread), and would still have the stability of quilting over tying.