IDK about the 3l, it seems that the largest engine the X1 can handle currently is the 2l. I would love to see a 35i or 35d trim, but it would have to be shoehorned in, from what I can tell.
As to the 3door idea, rumor has it that the X2 will be 3door.
http://www.e90post.com/forums/showthread.php?t=613098