sky_captain....From viewing the plans for the new pier D, I can not see anything to show that Pier C will be demolished. Looks like Pier D will sit snugly into Pier C as it is now.
As for the new Pier D under construction, there is a picture of it here ..
http://www.planepictures.net/netshow.php?id=527071
It appears to be running right beside the Temporary extension to pier A currently being used