Well the guys over at Hell Boy II: The Golden Army put out a great little video of the Character Design Meeting for Johann Krauss.
See the video [here]
They talk about how they need the moving parts of the suit to move. I love the use of a lazy Susan to give a swivel look and feel. Guillermo Del Toro also insists that he needs a mechanism that will allow his gaseous form to escape the suit quickly. Hence the disc located on his left chest area. I'm guessing that means that we will get an opportunity to see Krauss outside of the suit at some point during the movie.
For the curious out there, Johann Krauss was an exceptionally gifted Psychic who while traveling on the ethereal plane had his physical body incinerated. This was an incident involving the terra cotta warriors and thus the tie in with the movie, although I don't know wether they will show the actual disaster that incinerated and separated the souls of many around the site or if they are going to do a reinterpretation of the events.
The original incident left just an ectoplasm essence of Krauss since his body was incinerated. The B.P.R.D created a suit for him to keep him from dissipating. He has to keep his essence in a vessel or he will eventually dissipate and would be lost forever.