I don't think they're really secret classes, but more like planned classes I guess.
http://www.onrpg.com/boards/142348.html
Check that thread out, it has a basic wire frame of the possible characters. It also has some info about them i guess. I'm not sure about actual pictures.
http://www.youtube.com/watch?v=5iO8dy-7cj8
That is the old trailer I think dby2k is talking about in that thread.