Basically, that's impossible. You can't put a themepark attraction on public roads, nor can you create some kind of new custom vehicle and be allowed to use it, full of people, on public roads. If you did something like a normal bus with screens for windows like the train ride between parks, that can't be approved (I don't know the legality) due to safety issues if the bus is involved in an accident, how do you open the windows/screens in a timely manner in a way that children can operate. Let alone, how can you be sure of travel time to have any kind of experience running? Outside the parks, you have no control of the surroundings and have to follow all local and federal rules for the roads. If you have the outside world viewable, how do you tell people that you're traveling through the British countryside while they are surrounded by left hand drive cars, traffic, pedestrians, Applebees, and bars with everybody wearing shorts and T-Shirts?
Now, if you wanted to call any old bus a Knight Bus after you slap a body wrap on it and have a few TVs in there that people can watch with a 5 minute looping video, sure, that's doable. Not much of an experience, just typical public transportation with a targeted add being played the whole time.