I think Skull Island will be its own island. The construction walls might be there to help widen the path to the right (a teensy tiny bit, taking away some of the Camp Jurassic vegetation) to make more room for the Kong entrance area. The way the path twists and turns could do a Skull Island area enough justice to feel like its own land. Jurassic Park would technically start right at the Thunder Falls restaurant, directly after the Kong exit path merges into main path.