I'm actually more curious to see how the new megas affect the usage of the rest of the tier rather than the usage of the megas themselves.
I can't help but notice that a large number of the new offensive megas, specifically Gallade, Lopunny, Sceptile, and Beedrill, (although its safe to assume Gallade will rise/get banned) are all very weak to Fletch. Fletch OHKOs all of them, even without any prior damage, and bypasses all of their blazing new speed stats with its priority. Steelix is a pain in the ass, but its another counter that is severely crippled by WoW. It even wrecks a lot of the things that are likely to rise in usage (albeit slightly) thanks to new moves, like Pangoro, Slurpuff, and Gourgeist.
Bronzong could also could conceivably rise, since its an amazing counter to DD Mega Altaria (w/o Fire Blast), Mega Steelix, SD Sceptile and Sceptile w/o HP Fire, and avoids a OHKO from Glalie's Explosion and resists its normal coverage.
Granbull is also the best bet at a Mega Gallade check, taking only around half from +2 Psycho Cut and OHKOing with Play Rough. It also counters Mega Lopunny quite well, and can switch into Mega Beedrill's U-Turn repeatedly.
Spiritomb could also check Mega Gallade, albeit shakily, avoiding a OHKO from Knock Off (but needs like 90+ health) and neutering it with WoW.
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On an unrelated note, Mega Sharpedo seems rather underwhelming. A lot of people (not necessarily in RU) are over-hyping this thing, but I think people are overestimating its power by quite a bit. I ran a couple of calcs, and determined this:
Physical Moves: - ~15% power (in comparison to regular LO Sharpedo)
Strong Jaw Moves: + ~28% power
Special moves: - ~23% power
So really, only Crunch gets a power boost while the rest of Sharpedo's moves get a reduction in power. This is really mitigated by the fact that there are far more Water resists than Dark, but the reduction of power on its coverage moves can be detrimental in a lot of scenarios, specifically on Cobalion and Gurdurr. Also, even with the power boost on Crunch, its still doesn't have enough power to get past usual checks and counters like Alomomola, Aromatisse, Amoonguss, Druddigon, Tangrowth, other physically bulky things, etc. For example, even Doublade still isn't OHKOed by Crunch. Mega Sharpedo also lacks the ability to run a special or mixed set effectively, further exacerbating its inability to get past checks and counters.
The biggest drawback in my opinion however, is its lack of Speed Boost after evolving, meaning it really only has one chance to sweep. After getting a boost, it needs to be able to completely clean the opposing team, unless it is really slow. This is unlike regular Sharpedo, which can threaten out offensive threats with its revenge killing prowess early game if it needs to. And with the abundance of checks and counters (the only one really lost is Virizion, which is 2HKOed most of the time by Crunch now), its quite hard to sweep. Really, most of the things that stop regular Sharpedo can still stop Mega Sharpedo.
Then again, I might be underestimating it a little bit. I think that a major perk it has that people seem to be overlooking its its boosted bulk. While still as frail as shit, it can handle priority slightly better, notably surviving Fletchinder's Acrobatics 100% of the time, and has a high chance of surviving Lee's Mach Punch. This, coupled with the lack of LO recoil (which is also nice), really decreases the necessity of Aqua Jet, allowing it to run a third coverage move with much less opportunity cost. I personally think Earthquake is the preferred coverage move, since it can nail Cobalion, but Ice Fang is also cool, but still can't KO the bulky Grass-types and Gligar. Anyway, back to its bulk, it can also tank rogue Sucker Punches and the like, as well as switch into resisted moves if it really needs to.
tl;dr Mega Sharpedo has a lot going for it, but its not an extreme powerhouse by any means and makes much less of a splash on the tier than a lot of the other megas do