Blanchett as Spalko seems to have been great casting! Can't wait to see actual footage.
As to Mutt and Spalko duelling, if that happens, I'm sure Mutt gets thrown into the situation against his will and has to be rescued by Indy. But if that's not the case, fine. The movie can handle a fight scene without Indy. Mutt and Indy are on the same side, remember? But that don't mean Indy wouldn't be the main hero. You think Ford would agree to star in a Indy movie without being on center stage, not likely.