Bet on Mamoswine CD move and next T5 raid boss.
I'd bet that Mamoswine gets a Ground type charge move like Earth Power or something as power as other CD two bar moves, making Mamoswine best Ground type pokemon. And The legendary I'd bet to be Dialga, which only weak to Ground and Fighting. I seems Niantic often makes the CD pokemon raid-relevant pretty soon. For example, SD Ttar vs Zapdos and Moltres, Metagross vs Togetic, Feraligtr vs Groudon (cannot recall earlier). For Mamoswine, AV is already perhaps the best Ice type move in the game, and no potential T5 raid boss is weak to Ice (unless they bring Ray back, but still AV is powerful enough). So I would say Niantic will for the first time make Ground type relevant (although Heatran already caught our eyes on Ground), by giving Mamoswine a two bar Ground CD move and releasing Dialga.
Answers
I'd say that'd be good, however thes 2 problems, one Mamoswine is weak to steel, which dialga is, and two earth power would need to put mamoswine leagues above even Groudon to be on the radar for dialga counters. Right now Fighting types out DPS ground so heavily in neutral weather you'd never want to use them. Even in clear groudon's DPS is equivalent to machamp's, meaning for Mamoswine-clear to be a top contender it would need to be at minimum above groudon, and for neutral counter, far above groudon.
I'd like to see it get a great ground move, but that doesnt seem likely. Blast burn had similar potential to outpace moltres with Charizard, but it didnt happen. Mamoswine does have a very high attack stat, and even an average move likely would put it on over above groudon, given how bad EQ is, but it doesnt seem like it could become relevant agaisnt dialga unless its specifically Vs Thunder.
More likely I think the move will be ancient power.
I agree there has been a trend, but theres also just as many and more that havent, DP amphy, HC blastoise, FP Meganium, LR eevee line, BB typhlosion. But given how broad raid types are, most any moveset will be relevant against raids, given how many pokemon are in them
Heatran was only able to catch out eyes to ground as it was the first and so far only time ground was supreme since Raikou, the effectiveness buff also helped place ground far abolve everything else. In a setting where ground and another type are at equal effectiveness, neglecting weather, ground doesnt even register
Mamoswine had a greater attack stat than machamp, so it would take a move that is a ground clone of Dynamic punch roughly to place Mamoswine at machamp's level for a dialga counter (as machamp is the best and thus the baseline counter)
Groudon and Mamoswine ( if it gets a decent ground move ) will absolutely be Auto select mainstays along with Rhyporior in Dialga raids and are absolutely effective counters .... Niantic doesn’t expect the player base to have 12 maxed out Machamps if you haven’t figured out that Niantic and the vast majority of players don’t give a dam about Dps or using teams of supreme counters.... I simply don’t know what to say... and honestly for someone that can’t field a team of supreme counters for ANYTHING and struggled with tier 3 raids before the last two nerfs I would think you would take it a little easier on a Pokémon that will be in the top 6 of DPS and if not number one a close second in TDO
My money is on Ancient Power.
-First of all, it's the evolution requirement and I believe they will use it for the gig.
-Secondly, announcement mentions sinnoh stone reward for the weekend, Europe and Americas has the event on Saturday and they can't fully make use of rewards which is necessary for evolving during community hours.
-Thirdly, again announcement has ice puns and Avalanche is already assigned to Mamoswine. And I believe they won't be that low to event lock it's only ice charge move. It could have been the case if idk it had ice beam and got avalanche as event move. They might go overboard and give it Icicle Crash but I highly doubtful that.
-Lastly, they gave non-meta moves before (Surf Pikachu, DracoMeteor Dragonite, Dragon Pulse Ampharos, Last Resort Eevee)
Not that I want Ancient Power but rather just see it happening more likely.
I wouldn't exactly call draco meteor "non-meta" its still the second best DPS charge move on dragonite, while inferior to OR, its not by much. (theres also a window where DM actually preforms better than OR, though this time window is small)
But everything else, I agree there. I think it could get Ancient power, but icicle crash would be absolutely awesome.