Without taking nearly as much time to think about it as I'm sure you have...I'm seeing that dominate green and dark purple border around the middle of the quilt...I think it would be good to echo that around the outside of that center pieced part (which would be the borders that will be on top of the bed). Use the green closest to the quilt and the dk. purple on the outside. Then, between your corner blocks, come up with a pleasing layout of a couple of borders, maybe even a little piecing included in them, and then finish again with that dk. purple either as a border going all around the quilt including around those corner blocks or as the binding. I think any of the piecing in the border needs to be elongated shapes kind of like the long triangles/diamonds in the main part of the quilt. (Seminole patchwork and piano-key borders came to mind, but then I thought, that's way too square for all those long triangular pieces.) If this doesn't make sense, send me a private message.
Just my ideas, hope it helps get the creative juices going again. Your quilt is absolutely stunning. I love the colors and the detailed piecing. I've been quilting for years, but haven't attempted that style yet. I'm sure you'll come up with a beautiful finish. Please show us pictures of the finished product.