So in the lastest banner, Nubee confirmed about UR AW in the next update.
Well, we've already known about UR AW (and UR slayer) before they released Fantasy Archwitch. But now, it's confirmed. And the next AW will be UR!
Oh, and don't forget that AW will drop UR in the future! Maybe in the next update, I don't know >_<
EDIT: For someone don't remember, I spoiled that we will have UR Archwitch after they released new rarity - UR (it's also before I spoiled about Fantasy Archwitch). It's means long long time ago :(
At that time, we thought Harmonia is AW and Da Ji is Slayer (the fact that these cards hasn't been used for 4-5 events make us more sure about this).
Please don't force yourself to believe this. I can't confirm anything until they released Major Update.
Also, next AW is not necessary AW from the next event. It's may 3-4 events, maybe longer (like Harmonia things).