Apparently the DirectTV omnibus contract with Disney is up this month, September. So that may be why ATT U-Verse delayed in order to do all at once. DirectTV has already added the ACC Network as a one off.
But if all of ATT is up in September because of DirectTV rather than December, we may see ATT U-Verse add ACC Network in a few weeks. This will be good if they pull it off. May go into October, but I have no doubt Disney will get it done.
ESPN is already warning ATT subscribers and DirectTV subscribers that they may lose Monday Night Football if ATT holds out.