The reason why Disney hasn't expanded their monorail system or bought new monorail trains is because no one manufactures them anymore except as special orders. Replacing their current fleet of trains would cost roughly a half billion dollars and would require placing an order for at least 25 trains (they only have space for 12). Building onto the system to connect the other two theme parks would cost over a billion dollars as well. There is no return on investment (or at least none that could be shown to a board of directors or investors) so it will not happen until someone at the top of the organization say "this is what we're doing" the way Walt (and even Eisner) could. While it's a nice idea for Universal, there are cheaper ways to do it than a monorail. It could be an elevated transportation system like a funicular (like the Hogwarts Express is), but it will not be a monorail anything like Disney's.