From what I've heard, all off-site guest parking for Volcano Bay will take place on the first level of the south parking garage. Expect to see that level completely re-striped for added capacity. New toll booths will be added to both toll plazas, and the lanes will be slightly re-configured to accommodate the additional influx of vehicles. A new bus pick-up/drop-off area will be added on the backside of the first level of the south garage (the side facing Kirkman Rd.). New bus-only lanes will also be added, running along the perimeter of Universal's property from the south garage's new pick-up/drop off area to what's currently a retention pond on the south end of the Sapphire Falls plot. This retention pond will be re-purposed into the main bus drop off/pick-up area for Volcano Bay, with buses from the south garage as well as the on-site resorts dropping people off here. Access to the park from here will be via a tunnel/walkway that will run beneath the I4/Adventure Way ramps. Cabana Bay guests will have it easiest, being able to walk directly to the park from their resort.
Of course, all this could have changed over the last several months, but this was part of the plan at one point. No matter what though, you can expect some pretty major transportation improvements to start happening around the resort in the near future.
Also, look for Project 799 to start somewhat soon... the new Cabana Bay towers.