Volc, Mega Zam and Lucario are definitely the most threatening of the drops. All of the hype will be around Volc (obviously broken), but Mega Zam and Lucario will be in the shadows, seemingly not broken. But, let me show you these calcs:
+2 252+ Atk Life Orb Lucario Crunch vs. 252 HP / 252+ Def Slowbro: 299-354 (75.8 - 89.8%) -- guaranteed 2HKO after Leftovers recovery
+2 252+ Atk Life Orb Lucario Close Combat vs. 252 HP / 0 Def Filter Mega Aggron: 357-421 (103.7 - 122.3%) -- guaranteed OHKO
252+ Atk Life Orb Lucario Extreme Speed vs. 4 HP / 0 Def Volcarona: 157-186 (50.3 - 59.6%) -- guaranteed OHKO after Stealth Rock (you're going to see a lot of Lucario's ESpeed checks Volc and is necessary comments).
+2 252+ Atk Life Orb Lucario Close Combat vs. 252 HP / 252+ Def Chesnaught: 312-368 (82.1 - 96.8%) -- 18.8% chance to OHKO after Stealth Rock
Trust me, Mega Zam is a lot worse...
252 SpA Mega Alakazam Focus Blast vs. 252 HP / 4 SpD Snorlax: 302-356 (57.6 - 67.9%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Mega Alakazam Focus Blast vs. 252 HP / 252+ SpD Umbreon: 196-232 (49.7 - 58.8%) -- 74.2% chance to 2HKO after Leftovers recovery
252 SpA Mega Alakazam Psyshock vs. 252 HP / 0 Def Florges: 225-265 (62.5 - 73.6%) -- guaranteed 2HKO after Leftovers recovery
252 SpA Mega Alakazam Psyshock vs. 252 HP / 236 Def Florges: 168-198 (46.6 - 55%) -- 10.9% chance to 2HKO after Leftovers recovery
252 SpA Mega Alakazam Focus Blast vs. 252 HP / 4 SpD Filter Mega Aggron: 294-346 (85.4 - 100.5%) -- 6.3% chance to OHKO
Keep in mind, these are with a Timid Nature. With a base 150 speed, it can easily run Modest. The only relevant threat at that speed is Mega Aero. If you think oh, priority handles Mega Zam... oh no, your opponent is running RK Sash Zam, oh well. You're Absol and Lucario just got Focus Blasted in the face....
Goodra, Blissey and Ape are a good fit for UU, IMO. Blissey is annoying, but there are so many powerful physical types in UU (Heracross, Darmanitan, Mega Aggron, Mienshao, etc..) to take care of the pink blob. Goodra will be an excellent Spore Absorber and bulky tank with AV. Ape can go mixed and will be very viable. We may see Mienshao drop in usage due to the base 108 speed, but Shao can wallbreak with Reckless HJK, so it won't be dropping to RU anytime soon!
Alakazite, Volc and Lucario will most likely get the boot.