While Whispering Rock Psychic Summer Camp will not be a playable environment in Psychonauts 2, the team has recreated Raz's old stomping grounds in the new engine as a sort of sandbox for prototyping the sequel's gameplay and upgraded graphics. Check out the newly released video of Tim and project lead Zak McClendon playing this demo that we never shall.
Source: Youtube
I wouldn't mind it if they put this version of Whispering Rock as an extra unlock or something in the game (similarly to how the Broken Age lumberjack was originally just an art test, not meant for the final game).