I think they WANT to be in the same division. Here is why:
They will play as usual in early October for their regular season matchup, regardless if they are in the same division. So, suppose they are in seperate divsions and then they meet again in the Championship game. If the winner of the October matchup wins again in the Championship game, it eliminates the loser from the BCS. BUT if they are in the same division, the October winner wins the Championship and the October loser wins out they BOTH will likely go to the BCS just as it is now, only one will not be a conference champ. I don't think it really changes anything to have them in the same division and it is a win-win for the ACC.