If there is an EOS-1Ds Mark III - bating 'D3X' coming this year it will have quite a job to do to better the D3; possibly the most compelling, capable and well-rounded professional digital SLR ever made.
There was another iinteresting thread on dpreview about some guy that browsed around in the D3 update hex files. He searched for "D3X" and came up with 24 Megapixel menus, file size settings and options. I think the D3X is closer than we think. :)