Here's my reference point on our 28i X1 xDrive MSport.
1200 miles in and getting just shy of 28mpg in mostly highway driving. By comparison, our X3 35i MSport after 15,000 miles is returning 25mpg. Same 2 drivers, same roads and the X3 does not have ASS or EcoPro!
Still early days for the X1, but will be curious to see, and report, on changes to mpg as more miles accumulate.