I don't know of any instances where the FCC denied a request to shut off analog early.
There was at least one. In LA I think. That was pretty early in though.
The cable companies had all agreed to hold off tier changes and a few other things till after the transition to reduce confusion. Are their plans now on hold indefinitely?
The date for the change was picked to provide the greatest possible azz protection giving the politicians the most time possible before they have to go to the polls again. Remember last time they had a vote no one wanted to vote yes because they were afraid of the voters. If this gets delayed it could be delayed a lot longer than 6 months.