Hussey has been dropped from the T20 squad so there is a start.
Ferguson would probably be first in line for the #6 spot, I wouldn't be against Hughes batting there either to serve an apprenticeship like Ponting did before shifting to #3, Matthew Wade scored 1000+ runs last season and is probably the long term successor to Haddin, he is good enough to be considered on his batting alone, may be a bit early for him though. Cam White could be an option too if they let him concentrate on batting and forget his bowling, Usman Khawaja is a quality player as well.
Watson is pefectly capable of dropping down the order to let an opener in, Jaques will be back to full fitness and if he hits form he will be hard to ignore. Watson could also break down with injury at any time and open up a spot at the top.
Haddin could move to six with someone like McDonald or Manou at 7 but that would really be a big shift in selection policy for Australia, very unlikely to be used for more than 1 or 2 Tests.
It is a good time to be a young cricketer, a good start to the domestic season could open up some opportunities through the summer.