As much as I love the concept of retesting Ubers in OU (I was a big Deoxys-D OU advocate in Gen 7), I don't feel that it's really a great point of conversation at least until the DLC rolls around and we get more options. Pretty much every Uber Pokemon in the game at the moment would be too much for OU, and it would be detrimental to the meta to consider drops right now.
I've gotten in some talks with people on Showdown about retesting, so I'll summarize below how I feel about every Uber Pokemon that I've seen suggested for drops and why I feel they're too much at the moment.
Annihilape - Ghost/Fighting with Bulk Up + Tera and Rage Fist cleans up most team compositions late game with proper support. Far more powerful than people give it credit for.
Arceus Ice/Bug/any type - Arceus is far more deadly now than in any previous generation IMO - it has even more options and a much smaller pool of Pokemon to contend against it. Not even worth discussing for a drop.
Calyrex-Ice - 100/150/130 bulk with the most spammable physical STAB move in the game (Glacial Lance), access to screens, insane offensive typing, fantastic coverage, and Leech Seed + boosting options like Swords Dance? No, thank you.
Chien-Pao - It took a while to show, but Chien-Pao's attributes put way too much pressure on team building - it's literally Weavile on steroids, and Weavile was considered for a ban several times amongst the player base. Ubers is right where it belongs.
Chi-Yu - Do you want to have to run Max HP Max SpD Blissey or Clod on every team? Trust me, just don't.
Dialga (Base Form) - I've seen some semi-convincing arguments for this mon due to its exploitable Ground and Fighting-type weaknesses coupled with a lack of reliable recovery... until you factor in bulky sets with Tera + T-Wave, Rocks, and monstrous coverage + neutrality to other Dragon/Ice type attacks along with access to Trick for Scarf variants, Trick Room, and Bulk Up sweepers off of a very usable (and often forgotten about) base 120 attack. It's too versatile with stats that are too high for the tier overall.
Espathra - The Shaymin-Sky of Gen 9, kill it with fire and keep it out of OU.
Eternatus - Too fast and too powerful with access to Recover - STAB Dynamax Cannon means that non-Specs/Scarf sets don't have to rely on Draco Meteor, Sludge Bomb is additionally great STAB that nukes any fringe fairy options, while coverage in Shadow Ball and Flamethrower obliterates most of its checks. Additionally - Tera means that with Tera Blast it can turn the tables on Pokemon that would be able to handle it (however shakily), it's too much.
Flutter Mane - People can suggest Sucker Punch all they want until people start investing just enough EVs to live a Kingambit strike or run Tera-Fighting. This thing is way too powerful, fast, and bulky with great coverage and wonderful additional movepool options. Trust me, keep it in Ubers.
Giratina/Giratina-O - I get why there's pushing to test this, but the combination of bulk + stats with various movepool options for boosting like Calm Mind is simply too much - additionally, Tera means that Tera Fairy Giratina can waltz over most of its checks. It would put too much pressure and constraints on team building to handle it
Groudon - I've seen some people say that because Ursaluna is in OU, Groudon should be given a test - I could not disagree more. Groudon may not have Guts or Ghost Immunity, but it has 100/140/90 Bulk with 90 speed and a base 150 Attack - Ursaluna has 130/105/80 Bulk with a paltry 50 speed. Ursaluna has 140 base attack with Guts, sure, but Ursaluna also has a glaring Fighting weakness, cannot run Scarf if it wants to utilize Guts, is far slower, and cannot use Stealth Rock or Spikes. Groudon is essentially Ursaluna, but faster with the ability to set hazards and set up without reliance on status for power.
Magearna - No
Miraidon - Bulky Calm Mind variants effectively eliminate most of its checks barring highly specialized ones - Hadron Engine means that it cannot be hit with Amoonguss/Breloom Spore, Electro Drift is one of the most spammable STAB moves on the planet (which would lead to the most common OU variant likely being Tera Water with Calm Mind, Tera Blast, Electro Drift, and Draco Meteor. If that seems like an annoying set - understand that it also gets Flash Cannon, Dazzling Gleam, Power Gem, and Overheat. It's far too much for OU.
Palafin - People were calling for Basculegion to be banned because of its power under rain - Palafin has that same nuclear power, but can function without rain as well. Not worth it, keep it out of OU.
Volcarona - Extremely matchup-fishy and puts the same type of teambuilding constraints in place that Chien-Pao did. OU is healthier without the fire moth.
Zacian-Base - 120 Attack with +1 on the first switch in, access to both Swords Dance and Trailblaze along with STAB Play Rough and coverage options in Crunch, Close Combat/Sacred Sword, Poison Jab/Iron Head, and Wild Charge along with Tera. Not worth it, keep it out of OU.
Changing up the subject. I mean judging from what's revealed, we're just getting vanilla OU threats (or at least prior OU threats) what with Crawdaunt and Metagross gaining access to Terastallization. Testing has already been done for HOME so this is 100% possible. Going over some of your potential restests, here's my opinion on them and every other Uber rn:

If nothing is done to Terastallization, it can't be in OU under any circumstance unless Rage Fist got banned - however, as of now it's a signature move of Primeape & Annihilape. That move alone is why it's not OU. No restest needed.

Ok, MAYBE the bad forms of Arceus can get the boot. But like... can't it use Terastallization? I assume it can't in which case its
STILL too much to handle. Arceus Bug is the closest form to OU and even that is still an Arceus form. God shall not be allowed into the realm of OverUsed.

It's obviously overpowered. You thought Ursaluna was bad? Try it with
Moxie in favor of
Guts and the biggest attack stat in the game right now. Oh, and it has Swords Dance, Leech Seed, can set Trick Room by itself, can use Terastallization and is MUCH bulkier than Ursaluna. Hard pass.

You're joking. This thing is in Anything Goes my guy. U b e r s was a testing ground for this beast. You're sick if you believe this should be retested.

It's been banned from OU. Twice. I'm certain nothing can contain it no matter what happens.

HA! You really think a special attacker that can out Blissey is OU material? Yea go back to Arkham Asylum and chill out.

It's my favorite steel type, but its not allowed in OU for a reason my guy. It's got too many pros and not enough cons. IT EVEN HAS BULK UP!!!

Espathra. The biggest win more pokemon in this gen. Terastillization made it even more obscene to handle. But personally, I don't see the issue with it. It might be able to be retested so long as the tier shifts go against it. Maybe.

Eternatus. Lemme ask you this question: If a top 3 mon in last gen's Ubers is allowed in OU, what will happen? The answer: nothing good will come out of it. This thing is so obscene It's almost funny.

You guys that were here for the first 2 days of Scarlet and Violet OU know what this thing is. It's the ultimate special attacker, and proved to be unhealthy beyond comprehension. Speed, power, decent bulk - it all went right for the devious prehistoric Misdreavus.


I already mentioned it, but breifly: Maybe. It's not a good idea, but hey we like chaos.

No. Well, its managable... maybe. But I wouldn't recommend it. Plus it got Spikes and Will-o-Wisp support.

I wasn't totally sure why it was banned, but having unresisted STABs is not good for any tier. RNG be damned with the robo santa. Slim chance of unbanning.

Its Groudon with cons. And a free attack boost

I wouldn't touch this with a 10 foot pole with it being in OU.

Maybe. It's always very strong, and we just gave up testing it. But its still Landorus

I. Don't. Like. This. It will never be allowed in OU no matter what is said and done.

??? Probably not. I mean it's Mewtwo tho so

This is obscene. Absolutely not

I made a bold call saying its an Uber. It's an Uber.

The DPP legendaries are all hard passes - including Palkia.

Rayquaza. It's not mega, but its Rayquaza. You'd need some major power creep to allow this

The fastest ban in OU history because of Terastallization. If it goes, Regieleki is like RU

If Dark types can't take it on when it has no neutral moves, it's not allowed with Dark type coverage

Yea no. They're too much for OU to handle. Especially Urshifu Dark.

It's better than Kingambit in setup sweeping. I personally think its fine, but its really not

No. No no no no no. NOOOOO

It's kinda funny how Zamazenta Hero is OU and the Steel type version is Ubers. And it's staying there
When talking about Ubers in general, Theyre obviously broken. Them being in OU is so ridiculous the only answer is "..."
Oh well, so well. That's just how things are ig