Not sure I'd go with a full unbanning of Excadrill. Maybe throw it in some kind of limbo for the time being. What does it get? An extra check I guess? Not sure if that's ever been enough to make a mon OU
From what I've seen and experienced, Serperior is pretty crazy, but I think you really don't want to ban a DW mon unless it's just absolutely necessary (like banning chandy). Since, you know, DW mons are the entire reason for playing DW OU.