If I never again prewashed anything else, I would still prewash all Kona Solids. Kona is a 60x60 weave cotton broadcloth, a less dense weave than regular quilting cottons. It does shrink, but more importantly the hand changes with prewashing. The weave tightens up and it becomes softer. Prewashing also greatly reduces the fraying with Kona, again because of the tightening up of the weave.
If you want to avoid ironing an 8 yard length of fabric and aren't planning to cut anything longer than a side border, then consider subdividing your yardage before washing it and wash it on a gentle cycle to reduce any wrinkling. Prewashed Kona, including white Kona, irons flat (even without starch) and is not prone to inaccurate cutting. Will you be prewashing the rest of the fabrics in this quilt? That, too, may influence your decision about the Kona white.