The official announcement just arrived on my phone. Some important points:
"Plus, trainers can unlock an additional Charged attack to incorporate into their battle strategies."
This is huge. It now makes sense to carry a main move and a counter move, or a pair of attacking moves. Rayquaza carrying Outrage and Air Attack or Ancient Power would be difficult to handle, for example. Further, we don't know how these moves are selected. How does a trainer "unlock" the second move, what are the limits, etc. If I could teach my Gyarados Drill Run (highly unlikely) it would be a great counter move to oppose the electrics people will fight Gyarados with, etc.
I suspect that fairly soon this will carry over to Gym battles and raids. It won't be that useful for raids, since you know exactly what you're fighting. But it will allow many powerful raider pokemon to do double duty, being a strong option with two different attacks in a raid. For example, A TTar carrying Bite/Stone Edge/Crunch (or Smack Down/Stone Edge/Crunch). And for gym attacking, the attacker could mow through the defenders with whatever move works best. This will add some more strategy to the game, and will be a real boon for pokemon with two types and a good Charged move in each type (like many dragons, for example).
"Earn rewards, including a chance of rare evolution items, for participating in battle."
Looks this is how we'll get our Sinnoh Stones for a while. Hopefully also enough potions and revives to make PvP at least neutral on one's item list, if not a small gain.
"Ultra Friends and Best Friends can challenge each other to trainer battles from anywhere!"
That's awesome. I have friends from far away, and now we can fight whenever we want. I had originally envisioned meet ups where trainers gather to battle each other, much like raids, but lasting longer. However, Ultra friends now don't need to meet up, they can just make, say, Tuesday night league night, and from the comfort of their own homes, fight other trainers in fixed format or freeform tournaments. Whole new avenues of play will be opened up.
It's an exciting time to be playing PoGO. From the looks of it, they seem to be getting this one right. We'll see for sure when it goes live, and hopefully there won't be too many bugs (there will be some - prepare yourselves for that), and not too many bad design choices in the game structure. Hopefully they do something like separate swipe left and right, and make the new combat interface better, not worse.