I forget. What is the supposed "3D" supposed to be?
The EOS 3D is a fantasy camera that is supposed to be the ultimate combination of every bit of camera technology you could ever ask for in a relatively compact and affordable package.
Inspired by the film era EOS 3, which took every bit of tech Canon had at the time (zillion point AF, eye control, weather sealing, robust, high speed shutter, 100% viewfinder, EOS 1 series UI, etc...) and dumped it into a body that was just a little more expensive than the Elan (xx) series of cameras. Then Canon introduced the EOS 1v at over twice the price that offered one incremental benefit (bullet proof construction), but took away eye control and a little speed unless you bought the power booster grip. Note that every EOS 1D series camera since is based on the EOS 1v interface and PB grip-included cosmetics.
I would be willing to bet that the 5D III and/or its linear successor is about as close as we are going to get from Canon these days.