Darkrai gets a realistic monopoly on Sableye, the only way to re-use the broken Trainers we have. This alone makes it a tier 1 deck, whether it's used with Dark Trans Hydreigon or not. Eelektrik remains the most solid Energy acceleration, and while Junk Arm is a heavy loss for it, it can still discard with Ultra Ball and Juniper.
I'm glad Smeargle, Celebi, and Junk Arm are gone. Such explosive cards Vileplume I'll kind of miss, but without Junk Arm it's not as necessary anymore.
Expected viable/top decks:
Deck building becomes very different without Junk Arm. Small amounts of copies of Switch, PlusPower, Super Rod and other such Items need to be considered carefully. Bianca gets a role as the second anti-N supporter (Juniper being the first one), and has more potential with discarding cards like Ultra Ball, but Cheren is more consistent.