As I understand it, Sky agree objectives for each rider at the start of the season and stick with that plan as much as they can.
Personally, if I was Dave Brailsford, I'd tell Froome he needs to win some stage races before I was confident in his ability to win the Tour as he needs to show the team that he can cope with the pressure of leadership and expectation.
I think a very strong showing in Tour de Suisse or Dauphine would show if Froome is a top 3 for Tour!