when is the new improved xdrive system supposed to be implemented?

You mean the Dynamic xDrive? It will be after X6 release. As early as 2009 (1st facelift?)

^ you mean they might re-design the X5 again after only 2 years? Interesting... I kinda love it the way it is now.

7 years, normal model run, is a long time to wait if you've got new technology that wasn't quite ready for the launch in mid-2006. So, they batch the big things together and call it a facelift; generally done at the 3 or 4 year mark. Smaller enhancements are done along the way as the years pass.