I think this Trade exception is due diligence. If we got Barton or any other seemingly available veteran, it would take the ball out of our young guys hands (Smart, Rozier, Brown, Tatum). What we can get for that money is not a significant enough upgrade to limit our young guy's development, especially in a year where we are given to opportunity to develop the young guys.
The exception is a resource, an opportunity, or another tool in Danny's arsenal, even if he doesn't use it. If there is another injury to a veteran (Baynes or Horford), I can see us making a move to get a veteran big who can run the pick-and-roll with Irving. Otherwise, I think the exception probably eventually just expires.