The summit will indeed be located inside Stage 17 at Hollywoodland in Disney California Adventure. It's the building between Muppet Vision 3D (which is now the home to For the First Time in Forever: A Frozen Sing Along Celebration), and the Monsters, Inc. Mike and Sulley to the Rescue attraction. The last time I visited Stage 17 was when it was Olaf's Snow Fest. Can't wait to see what it will be like inside for the summit!
Also, I hope we get some time to visit the park itself, especially since my favorite dance party, the Mad T Party, is right outside the building.