I know that LurchBrick has mentioned SDL as a replacement for MFC. I don't recall anyone mentioning OpenGL, but that doesn't mean it's ruled out.
Right now, all of this is post 1.0. We first want to finish the original goal of Dungeon Craft, and then we'll move on to the updating.
I think changing the way that walls display, i.e. switching to 3D from pseudo-3D would be way cool.