No sorry 4x8 is the maximum size, which fits quite nice into his room. Thanks for the link, your fortress is just MASSIVE :-)
The plan is to put the playtable on top of some cardboards, so it's the perfect for him to store other lego and play on all four corners with his friends.
Good for me that I still have some years to plan it, he is still busy playing with Duplo ;-)
Sample image of lego playtable: