The swap of Unholy Blight and Summon Gargoyle is an interesting one because Unholy PvP builds skip Unholy Blight to begin with. Even with the nerf to the extremely powerful Gargoyle in Patch 3.0.8, Unholy Death Knights continued to pick up the talent, partly because it was high enough in the tree, and partly because it still gave a considerable damage boost. Patch 3.1 will buff Gargoyles again, which means Unholy Death Knights will have to commit deep into the tree to pick up one of the more powerful burst talents available. Hopefully, with the removal of Shadow of Death from Arenas, Blizzard can lower or remove the cooldown, or not make it a requirement for Master of Ghouls.
Although Unholy remains the most popular PvP build, Blood is an increasingly popular tree, and gets some notable boosts in Patch 3.1. Sudden Doom is a great passive damage boost for Blood in PvE, but can gives frightening burst potential in PvP. One curious change is the revision of Blood Gorged to grant Armor Penetration instead of Expertise. Pending some foreseeable changes to Armor Penetration in Patch 3.1, this looks more to benefit PvP right now.
There are proposed changes to the Frost tree that we'll have to see to determine if it becomes more popular for PvP. Right now, there are some pretty good Blood / Frost builds that work around Hungering Cold, one of the best peels in the game and works like a Mage's Shatter-combo with Howling Blast. So that more builds can pick it up, Endless Winter will be moved up to the top of the tree, hopefully along with Chillblains. This means Death Knights, who are already hard enough to get away from in PvP, will be even harder to shake off.
One of the changes made across the board was the revision of Armor Penetration to work of percentages rather than a fixed amount. Similar to the change in mana draining mechanics, this change is intended to balance out armor reducing abilities. This means Faerie Fire will work better against plate and no longer as hurtful against cloth. Tree Druids can now cast Thorns, but more importantly, Nature's Grasp. This should contribute somewhat to survivability and self-peeling.
The passive talent Savage Defense, even though it's clearly intended for more Druid tank mitigation, will help desperate Druids everywhere -- who pop into bear form when their number's almost up -- provided they crit enough. The change to Survival Instincts, now usable by Moonkin, makes no sense at all. I guess it's nice, but Balance Druids go up the Restoration tree for supplemental talents, not Feral, even for PvP. Overall, none of the announced changes to Druids so far have significant impact in PvP. We have yet to see Feral and Balance achieve the same representation that Restoration -- overwhelmingly the dominant spec -- has in Arena play. I fully expect Blizzard to announce some changes in that direction in the coming weeks.
No more ammunition. That's huge. Hunters are probably the only class that incurs costs when doing some simple PvP such as dueling. The removal of ammunition allows the enjoyment of Battlegrounds without the added cost of replenishing bullets or arrows. The change to Piercing Shots to induce a bleed effect rather than armor penetration is something of a PvP nerf damage-wise, but raises sustained PvE damage. On the other hand, a bleed effect is just the thing to keep Rogues visible.
The rework to Sniper Training is a PvP nerf, if anything, because Hunters almost never stand still in the necessarily mobile PvP environment. Aside from fights such as Patchwerk or Instructor Razuvius, I can't imagine the talent being useful for PvE, either. It was insanely powerful in the Battlegrounds, but the change makes the talent even more skippable. I'm excited to see what "additional trap functionality" will be added to Survival, specially the promised 41-point talent spot currently occupied by Trap Mastery. If anything, those promise to be good -- or creative -- for PvP.