So I'm just gonna leave some thoughts and feelings right here about the meta and what i think about it with the addition of some new megas and a few changes to movesets ^_^
Let me start with the megas:
Mega-Altaria;
First impressions of this thing, it's hard to stop if it gets going, it takes little effort to use, it's 1000x harder to play against than anything else in the tier. it's typing means it's a switch in to fighting, no more rocks weakness, reliable recovery (which is godly for its defense stats) along with heal bell + dragon dance. This thing is a monster, a complete fluffy monster that in my opinion is far too good for NU, it's a mini-mence that has better typing. It has OU potential, not sure why it should ever stay around, have fun abusing! xD
Mega-Sceptile;
In my opinion, trying to build any team right now in NU is so centralising to the fact that this grass dragon that is no longer checks by physically defensive poison types or dragon types means it's so so so hard to beat. Its base speed is really fast, it can even outspeed modest gorebyss after a shell smash with max speed timid/jolly. It has no set "counter" in my opinion but only a few checks, (I'm going to ignore things like maril). Things like hariyama, muk, mega-audino do a good job at checking, however the set variety is so big since it can run SD + EQ to beat these special checks and could even run mixed with leaf storn minimal speed investment because it's already so fast and bop the switch ins xD It's really a good mon, does sorta lack a bit of power to get the final kills it needs though since no life orb but still a reaalllyyy good mon and probably the most threatening mon behind altaria when team building imo. Although there is sheddy to beat it reliably however it needs so much support that I just don't want to build a sheddy team personally xD
Mega-Lopunny;
Now i've heard a few people say it should be quickbanned, but from personal experience and use of the pokemon, it's not thaaatttt good o.o Psychic types beat it very well, like musharna, uxie etc since it has no knock off to spam! I know from experience that this means it's not even that threatening and it goes back to the BW2 meta where musharna countered sawk etc, it's basically the same with this mon xD along with that, you also have poison types like weezing, garbodor, that can take hits (not as well as a defensive musharna or uxie) but they are still answers. As well as this, it's slower than both mega-sceptile, mega-beedrill which puts it in an annoying speed tier in comparison. If you take those 2 megas out, it destroys all offense :L But as far as I'm concerned, there are stops to this mon and they can put in work! So I'd put it behind sceptile and altaria on how good i think it is xD
Mega-Beedrill;
Now again with this mon, it's very very weird and odd. From both using it and playing against it, it's annoying. If it manages to get a reliable mega off, it's an absolute pain and complete momentum booster for offensive teams in general and shits on teams without a weezing. It seems however i don't think i could fit it on balance since it's far too frail, it would never be a switch in to a CC or fighting types since it's just too frail to risk the knock off or coverage move with paper thin defenses. But on the other side, if you can't mega it up, it's almost useless. You may have to be forced to use protect on it to do any damage to teams reliable which cuts its versatility with coverage moves, but who cares when you have dual stab adaptability. Along with this, there are also a couple of set ideas I've noticed, since it learns swords dance, teams without priority could be destroyed by this thing as a sweeper, not just a momentum grabber with u-turns. In general i think it's very very good, up there with the best pokemon in the tier, if it wasn't for weezing i would say there's not counter but since there is, i feel like i have to run weezing on a balance team to prepare for mons like beedrill, so hence very centralizing like sceptile.
Mega-Audino;
Now this is probably my favourite mega so far. Cro-dino is a veryyyyyyyyyyy good pokemon right now, it's also very fun to use. It's not broken by any means, it is so bulky though, reliable recovery and cool stab moves with dazzling gleam plus calm mind making "cro-dino" one of my favourite pokemon right now. If beedrill were to leave the tier perhaps, it would be a lot more popular, however there are still a tonne more checks and counters running around in the form of the poison types like muk, weezing, garbodor and even things like mega-steelix, klingklang, pawniard etc etc. However, I can see a lot of potential for this mon with some team support (I know, a phrase I haven't used yet with the other megas O:) that you can sweep with cro-dino. I'd love to see this mon get some more love since it's a really good pangoro stop (doesn't appreciate banded gunk but oo well) and in general a fun mon to use.
Pangoro;
Now I've gone through the megas, but this mon also got some amazing buffs that make it so good right now that it can destroy balance and stall teams with its sheer coverage and power. Since it gained iron fist drain punch, knock off and gunk shot, it's honestly just what this pokemon was lacking. It's really good now, realllllyyyyy good. It can fit on teams nicely as a banded nuke or even the taunt-sd set which sets up on things like weezing xD It's even got recovery with drain punch that makes it hard to stop, which means you have to sack something to deal with it, so it will most of the time assure you 1 kill xD it will probably get taken by RU by usage, but a really fun mon nonetheless, i will use him myself while i can! xD
Slurpuff;
Now this mon is probably the most threatening regular mon around right now. If it sets up and has more than 30% hp left, it's almost impossible to stop. Drain punch makes it soooooooooo much more threatening. I've even played a game where I had a fake out mon (lopunny) but couldn't even do 25% to it, hence it recovered up with drain punch and made the fake out damage pointless, which means that priority isn't stopping it reliably right now. It is only stopped by poison types, which makes it really centralising, in all honesty i hate playing against it as it is such a threat, it can sweep teams effortlessly. Use it while you can! I can't see this staying around too much either xD
In conclusion to ma thoughts + opinions, I'm gonna have to say that only a few megas will likely stay in nu, those being mega-steelix, camel, glalie. Even Audino I think will eventually have some "ban-worthy" qualities soon enough xD So hopefully once the meta has settled, it will be easier for people to team build again! xD