If North fails now, IMO Watson should move to 6, Hughes coming back in to open again.
I'm all for Watson batting at 6 for Australia, and bowling the few odd overs. Opening, or bowling more than 15 overs per day, if a big no no. Whilst he has performed decently once, I don't think that he is up to it. If he goes on and makes a ton, and a couple more fifties, before this series is out, I still won't be convinced. When he backs it up with consistency after a couple of series, then I will be sold that he is a genuine opening option in the longer form.