That sounds very interesting, you are right to film the book it will require quite a big budget especially this is when you want to reflect historical characters and the place where the events took place. I like idea of visiting the Asia and join Marco Polo, always were inspired and really impressed with his biography. I can imagine how the Dr. Who team would be interacting with them. I hope may be one day BBC decide to film it is a great story and a lot of adventure :)