So Biggest New Threats Include:
Haxorus+Aqua Tail(Is Aqua Tail Better than what Fire Punch would've been?)
This.
We were clamouring for Fire Punch based on super-effective coverage but Aqua Tail + Low Kick/Superpower turns out to be pretty awesome.
I'd loverlooked Low Kick the first time. It nails Ferrothorn almost as hard being 100BP against it. +1 LO Low Kick has a 53% chance KO max Def Ferrothorn (which is not the standard set) with SR. So for sweeeping sets that'll hate Superpower's stat drops it's a pretty good alternative.
Aqua Tail lacks the SE coverage of Fire Punch but has higher BP and Haxorus gains pseudo-STAB on it in OU's most common weather. When you have 432 attack even before boosting, SE coverage is a lot less important.
Choiced sets will probably be the most common esp. CB Haxorus. It can KO/2HKO any Pokemon in the game with the right move. In the right weather Skarmory, the only safe switch-in Haxorus formerly had, risks being 2HKOd by Aqua Tail. And with the new options, it won't be as easily goaded into locking itself into Outrage.
DD sets have a bit of 4MSS. Outrage and DD are a given but he'll have to pick two from Aqua Tail, Earthquake and Superpower/Low Kick. The Fighting move should probably get the nod over Earthquake if Haxorus has rain support. But nailing Rotom-W with Moldbreaker Earthquake rather than *having* to Outrage is nice. +1 LO Superpower also KOs but it has obvious drawbacks on a sweeping set. Low Kick has no chance since Rotom is very light.
But I think Haxorus' main niche will be as a brutal wall-breaker with CB. If it comes in safely on a slower Pokemon chances are good that SOMETHING IS DYING. This is significant because it now fears little from most Ferrothorn and immediately threatens with Superpower. This dragon will be getting a lot more use.
On another note, it might be a good idea to experiment once more with Excadrill and Garchomp. They might be good counterbalances to the rain's new terrors and we'd get another good rapid spinner. Though I can foresee complains because Iron Head is like a more powerful Return which can flinch (along with Rock Slide...lol). Is Techniloom out yet? It's a general terror to sand, threatening both auto-inducers and Excadrill. I think we can have a balanced and fun metagame with all those Pokemon in it.