In a meta where offence will be king, you need the offence killer. You need weather! Let me introduce you to your candidates!
Sun
Torkoal - Scovillain - Slither Wing - Chi Yu
Sun will obviously stick out at the start due to how it buffs up all the new caveman mons. Torkoal is your setter. It hates the lack of removal but hey what ya gonna do.
That weird ass pepper mon Scovillain has just about the right stats and movepool to work as a chlorophyll sweeper. 108 SpA ain't incredible, but it's good enough when sun boosted to smash hard. Growth, Fire Blast, Solar Beam/Giga Drain/Energy Ball/Grass Knot for grass stab to hit rocks and waters. Unfortunately its special movepool is pretty lacking so there's no good final move on a special set to hit fire types. But mixed works since you can run stomping tantrum. It's physical movepool is much better overall, including Zen Heatbutt and Crunch, but is stuck with fire fang so isn't worth it. Honestly you hit so hard with fire blast that you could run sub in the final slot.
Sun mons amongst the Caveman Mons are tough to pick out since the obvious candidates would be banned even without sun (Salamence and Misdreavus). From the remaining candidates, the extra floofy Volcarona looks promising. Its attack is so high so it can't realistically boost speed, but you do have flame charge as a genuinely terrifying option. +1 speed and +1 attack floofy bug will sweep a lot of teams.
Finally as just a fire type nuke, hard to go wrong with Chi Yu. I actually think this mon will take a while to get banned, since its 100 speed will look slow compared to the hyper offence at the start, it has no good speed boosting option, and hates the numerous dark types the starting meta has. Still, if you just want to click funny fire button go boom like Victini or Darm, Chi Yu is probably your best bet. (I guess there's Zard, but eeehhhhh with hazard control as difficult as it's going to be, not convinced Zard will be a good option).
Snow
Slowking - Cetitan - Abomasnow
I'm rushing in here excited to tell you all about my new favourite combo: Slowking + Cetitan! Slowking can do the frosty teleport move to bring in Cetitan for free under snow. Since you'll want to try bring in a physical attacker versus Slowking, and not one who is a fire or fighting type, Cetitan will be in a perfect place facing something that will do not that much damage to it with its defence boost in snow. From there, Cetitan clicks belly drum, runs the old ice+ground super duper Mamo combo and dunks on everything. You can't even revenge it in snow with mach punch Breloom since Cetitan can just click ice shard for its last move and out-priority the priority.
There's also the option of Abomasnow, which isn't as laughable as it sounds originally. The defence boost goes a long way to making it much bulkier. It means it switches in pretty freely versus the Chad Dolphin. Plus it's going to be one of the few mons that take not much damage from Future Delibird, since it resists hydro and takes little from freeze dry. Considering how good Veil is, it's not a terrible option. However if you want screens + hail for the optimal Cetitan setup, Slowking can actually do that too. Run Oblivious over Regenerator if you are going dual screens to hard commit to the strategy. A bit silly but definitely viable.
Sand
Tyranitar - Hippowdon - Houndstone
I don't see a huge amount of space for Hippowdon in OU right away, but TTar definitely can fit in. But what is he going to do without his best buddy Excadrill? Team up with a good doggy! Not Lycanroc you silly, although I suppose if you squint really hard you can see a niche for it. No, it's with Houndstone. What does Houndstone do? Well, you know how Dracovish couldn't have Strong Jaw and Sand Rush at the same time, so you were "stuck" with "only" the 170 base power version? Well fear no more, because Houndstone has Last Respects, the 50 bp move that gets an extra 50bp for every mon of yours that faints. Meaning it's not difficult to see a last mon Houndstone under sand easily sweeping teams with its funny 300bp kill everything move.
It technically has coverage for all the darks with Play Rough, but let's be honest here. You might as well only run two moves on this mon, and the second should be Sleep Talk.
Rain
Pelipper - Barraskewda - Drednaw - Palafin
Rain is kinda shit out of luck. Yeah you have Pelipper, but Barraskewda lost flip turn in the generational shift, and Skewda without flip turn dropped to RU in Gen 8. Your best swift swim sweeper is Drednaw. Drednaw! I've actually used Drednaw in UU and it's not that bad. It's pretty much exactly the same as Kabutops (SD + Liquidation + Head Smash + Megahorn). Your best bet would be using rain to boost hard hitting water types like Palafin or maybe Quaquaval? That is, until Home is released and we get the Hisui mons. There's Overquil, but you also get the unholy abomination that is Basculegion for the brief 5 seconds before it's banned.