David,
I'm in the same boat as you. (I have a two week old right now). If you take a look at:
It looks like there will be plenty of room for a rear facing seating. On top of that, the trunk is larger than a 1 Series (which is what I have) and a stroller fits fine (Baby Jogger City Mini) in my trunk.
Here is a photo of a rear facing seating in my 128. I'm 5'10.
I can only imagine that the X1 will provide a bit more space in the rear (now, not the same size as a X5 or current X3) since it's based of the E90 chassi.
You can also take a look at:
http://e84.xbimmers.com/forums/showthread.php?t=708958 for a video walk-around..
The 128i does a good job to be honest, the X1 would do a better job though.