I'd be tempted to audition a fairly wide white border with a wave or scallop edge, then bound in a solid pink or deep rose.
While piano key borders can be fun, I think there would be several downsides to using one on this quilt.
For one thing -- you've got so much already going on in terms of color and pattern, the piano keys would just be a distraction. No matter how you cut them, they'd look thick and clunky compared to all that tiny piecing.
Also, I personally find that when I have a lot of small pieces in a quilt top, it tends to have a lot of "give" and I like a border that is fairly stable that won't also be heavily pieced and prone to stretching and distortion.
A lot of times I skip the border and just add a binding, but this is a quilt that will look nice with something to contain and frame. I also like the idea of continuing the piecing up into the border. Another idea -- depending on how much more time and energy you want to put into the quilt, you could do an applique border -- something like a vine with flowers in some of your colored fabrics that extends out from the corners.
What I would probably do is finish the piecing, then photograph the quilt top and print out several copies. Then I'd play around with adding borders in several differnt styles to my print outs, and see what feels right.