As much as I enjoy the studio tours personally, and I've done the Universal Trolley one, the private tour, Warner Bros Tour and the Paramount Pictures tour I don't see the Universal tour expanding as it is very disruptive to shooting on the backlot.
We rented part of the European Square for a commercial shoot, and even though it cost around $15k to shoot there, we had to stop every 15 minutes or so because the trolley tour came by and went into the King Kong ride, which was very loud. Not an easy environment to work in when you're recording sound. They drive all over that lot so it makes life hard to film there. But I am sure they will shut parts down, like wisteria lane etc when large production rent out the whole street, but they're still very loud when they roll by with the tourists.