Hello Lorenzo.
I suggest you put your idea about the extension of the line in the comment of the original DPS route. Since I don't know how to load real world terrain to a route it's not possible to me. I am sorry about that.
(Not sure, but I think you can buy and dowload the route between Newcastle an Edinburgh from Just Trains)

Best regards.

Can you extend the route to other destinations, please? I suggest you to create the route between Eaglescliffe and York and between Newcastle and Edinburgh