This is a dumb idea for a couple reasons.
One: It's a clear ripoff of the Demon, which is made all the more apparent by the fact that he's getting this gimmick while feuding with Finn Balor himself.
Second, we all know Finn is destined to win this feud. He basically already has, but it's still going for some reason. Anyway, you're going to debut this thing only to job it out in the first or second appearance? So not only is it a ripoff, it's a ripoff that you're going to establish isn't nearly as good from the get-go.
Third, you know fans have been speculating/anticipating the reveal of an actual Sister Abigail for years. As in, a female wrestler who plays the Sister Abigail character. So they should know that when they trot Bray's ass out there in a wig and makeup, looking like the girl from The Ring after one too many trips to Golden Corral, people are going to shyt on it. Hard.
It would take booking on a level WWE is not capable of for this thing to not be DOA.