Calm Mind Reuniclus is gonna be a massive threat; it can use Shadow Ball and Focus Blast for perfect coverage, Recover combined with Magic Guard and lefties for great lasting power, and it no longer is threatened by Scizor's U-Turn, Heracross / Escavalier's Megahorn or Tyranitar's Crunch. Alakazam will be a faster, more offensive option which would also be much less hindered than most offensive pokemon by this metagame; an offensive set of Charge Beam / Shadow Ball / Focus Blast / HP Fire anyone?
I'm predicting stall to become much more viable - which is why I expect Calm Mind Reuniclus to become a massive threat in the much less offensively-oriented metagame. Blissey and Chansey are completely unhindered, Ferrothorn is only disallowed from using Gyro Ball and Power Whip so it is still a great staller / wall (and Forretress is also similarly unhindered), and Sableye will be much harder to kill with things like Draco Meteor, STAB rain-boosted Hydro Pumps and STAB sun-boosted Fire Blasts banned. Some offensive Pokemon - like Volcarona, Breloom and Scizor - are almost completely useless now, while others like Tyranitar, Dragonite and Starmie are hindered but still have some good options. Wallbreakers are gonna be incredibly rare, with only a select few Pokemon like Dragonite even able to mount a significant offensive threat anymore. Stallbreaking is gonna basically consist of Reuniclus and Sableye (and possibly Crobat) trolling the hell out of the much more common stallers and walls in this metagame.
Basically, I'm predicting most offensive Pokemon that primarily rely on STAB moves to be almost useless, while ones that have great coverage and utility - Dragonite, Hydreigon, Alakazam, Nidoking and Starmie in particular spring to mind - to get great boosts in usage. Stall and stallbreaking are gonna get MASSIVE usage jumps as hyper-offense becomes basically non-existent. Oh yeah, and every single Rotom Forme is basically gonna die off out of existence.