If you look at the Honda Odyssey http://automobiles.honda.com/odyssey/interior.aspx
, their 2nd row of seats has impressive flexibility. One of the things you can do in this car is have 3 car seats across the 2nd row. Not too many cars have the space or the attachment point to do this!
I'm hoping the Model X will have 3 car seat attachment points in the 2nd row, and a total of 5 attachment points for the whole car!