So I've had a couple of days to play around with hail, and here's some general observations:
-the tier is already equipped to handle this new weather, tons of great mons who already see plenty of usage are ready made counters and annoyances to hail
-Golurk in particular is brutal for hail, as Snover/Sawk/Duosion/BlizzardSpammer, a common hail core, has no real way to break through it. Golurk is so good against hail I think a Pursuit trapper or Sucker Puncher is needed just to stop him
-On the discussion that CB Sawk is much more useful than Scarf Sawk at the moment, I'd tend to disagree simply because of the Scarf's version to revenge kill threats, especially in Hail. The biggest reason to use Scarf is that Sawk outspeeds Cincinno, and it's unbelievable how many times an opponent will leave it in against Sawk, in my experience
-Otherwise Sawk is everywhere, but thanks to being a very straightforward Pokemon, is very containable. Right now it's a lot of fun to use Mold Breaker and Earthquake switch ins like Haunter that used to come in with impunity.
-I played Hail in Gen IV UU and some OU where basically slapping on pivots and two-three hail spammers were all one needed. This generation I'm surprised that Glaceon, such a dominant presence in hail last gen, is shockingly mediocre in the depths of NU. With so many fighting types and overall heavy hitters, Glaceon just doesn't last and misses the power that Specs would provide (since I generally need Scarf to be fast enough)
-The best hail teams are the ones that generally take advantage of hail as residual damage and some blizzard spam, but have at least 3 Pokemon (preferably four to fill all the gaps) that don't use Blizzard at all. In other words, Hail seems more effective as a complimentary battle effect, rather than offensive abuse like Sun/Rain
-Duosion is an absolute monster. Eviolite Max Defense Calm Mind Duosion seems to find all kinds of time to come in and set up. Really appreciates Golurk taken out though (I'm going to test Mawile as a partner, since it is a fantastic Golurk lure)
All in all, I'd say Hail is far from broken from my initial testing with and without using a hail team. While I have a feeling Snover will end up moving to a higher tier due to usage, I honestly have no problem having hail in the tier. It brings new mons into the limelight, and spices up an already diverse tier.