Some thoughts about BH
mega steelix will be a really, really solid pick. Able to run regen vest, soundproof, and fur coat sets without having to worry about nearly as much crazy stuff as before is really going to help this thing. Aggron mega is in a similar boat, but unfortunately it has lower SpD and is still bopped hard by volt switch, which will probably be more common thanks to galvanize users' increased use.
Mega salamance: Without mega ray this arguably becomes the aerilate user to beat, though it looks like we lost a lot more offensive mons than defensive ones, so the metagame will be more defensive in nature. That means that things like Mega Steelix can tank boombursts fromthis thing all right,. Tohgh actually, Charizard-y may perform the aerilate specs boomburst role even better, but it's also slower by several tiers. Something to try out, I think!
Alacazam-mega: not a bad substitute for MMY but you have to make sure that you OHKO what you're hitting or force a switch, or you will die from u-turn damage.
Mega swampert is probably the best or second best Fur Coat wall in the tier, only really having to compete with Mega Steelix and Groudon. Though Steelix has overall more resistances to physical attacking types like flying and bug, and a higher defense stat, Swampert does give you a fire resistance, no nasty fighting vulnerability and the ability to take a surprise special water attack. yes steelix is bulky enough to take physical water attacks,. Swampert however, cannot really take more than a single grass attack. Both of them are totally immune to Electric which already makes them great against Zekrom. Groudon has fewer resistances than does Swampert, but no double grass weakness.
Mega Blazicon will probably be a very popular pick in this tier since it no longer has to compete with Groudon for a teamslot. It has a lot more weaknesses than does Groudon though, and its ublk is total crap, but physical contrary sets will defeinitely need to be prepped for.
Standard Kyogre and Groudon will also be very respectable options. And it never says that the orbs are banned, so I can see red orb groudon doing solid damage, though Fur Coat walls Swampert and Groudon will keep it in check since it can't run a bosting item or ability, so special sets are a lot easier to deal with. PH Kyogre will be an annoying wall to take down, probably requiring a strong electric-type to counter, since we've lost one of its best grass-type checks in Mega Sceptile. Core Enforcer will also make it difficult to sweep.
Lucario mega takes Cartana's place as a fast offensive Steel wallbreaker. I could see Technician being ran to take advantage of its 145 attack plus STAB Circle Throw and Gear Grind to blast through non Fur Coat Steels and bulky Fairies such as Diancie and magearna. But don't overlook that 140 Special Attack that lets it run a special attacking set running blue flare, Aura Sphere/focus blast and Doom Desire/Flash Cannon. It can also sweep with Shell Smash, and if you add a focus sash and have Psychic Terrain support or DQM, you can power up a 200 bp stab Reversal. What fun!
Metagross-Mega is a more offensive take on the Regen Vest pivot, with that beastly 145 Attack it can easily switch in on Mega Alacazam and Pursuit trap it. A Belly Drum set isn't too unviable on this thing, especially since its typing gives it protection against three of the four -ate priority moves and it still has 150 base defense after setup.
Garchomp-mega is a powerful Ground-type attacker, and will be able to offensive check Red Orb Groudon if it hasn't boosted its speed. Though with the absence of a lot of bulky dragon types like Giratina and Zygarde-C, its Dragon STAB is kind of superfluous imho. I would definitely try running it as a tinted lens wallbreaker, though the Poison Heal sweeping set also looks like a really solid pick. It must watch out for Weavile, which will be a popular Refrigerate user, core enforcer users as all PH sweepers need to do, as well as random ice coverage on things, but I think that a lot of mons won't bother to run Ice coverage unless it provides them with neutral coverage, such as bolt-beam. Why, because there is no Zygarde-C or Giratina.
Standard Rayquaza is an acceptable Aerilate attacker too. It has better attacking stats than does Salamance, but worse defenses and a lower speed, which is why Salamance is probably better, especially since I imagine games will be a bit slower. Longevity is key. You can also run Dragon Ascent and an item to get Mega Rayquaza, but Delta Stream is not a great ability so it's probably not worth it.
Heracross-mega has the highest attack stat in this metagame and can put it to go use with Triage or Refrigerate sets. Unfortunately that junky base 75 speed holds it back from actually sweeping through things, nor does its STAB coverage that's resisted by Fairy, Ghost, Poison and Flying. It's probably better as a revenge killer.
Toxapex doesn't look all that bad either, as it is able to Leech Seed stall a lot easier now. Also cool is that a lot of top Dark-types such as Yveltal and Greninja aren't here anymore, so it can use Prankster moves a lot more successfully. Slow speed means that it also shrugs off Core Enforcer. The water/poison typing lets it resist Pixilate and Refrigerate moves, as well as Steel and Fighting moves. But just watch out for Psychic Surge Alacazam that will just blow it away. Definitely an interesting pick.