The PvP Souls only have 21 points available, actually; I was focusing on getting my 4 characters all 8 PvE souls, so I was unable to farm enough points to get the PvP souls, but from the information available on the official site and in the talent calculator here, you get 4 different focuses in each PvP soul and are allowed enough points to fill out one focus.
Mages get an anti-healer focus, one for pure output, one for survivability, and one for CC immunity. Rogues get a mage-hunter focus, pure output, one for sneaking, and one for survivability. Clerics get CC immunity, healer hunter, pure healing tree, and support healer tree. Warriors get a tank-ish focus that buffs their blocking skills and allows them to block without equipping a shield (IE, blocking with a 2hander or while dualwielding) and caps with a 50% raid shield; their other trees are survivability, berserker mode where allies taking damage increases your rage/damage, and a build for CC immunity.
According to the talent calculator, you *are* able to sacrifice points towards one focus to put points into another focus, but even one point sacrificed means you cannot get the focus itself, and all of the focus abilities are too powerful, and the leading-up talents too weak, to make this even worth it in the slightest. Yes, creativity is key, but there are 4 paths to take, allowing you to customize your PvP soul to a great extent; don't waste points on the PvP soul unless you take a full focus, your other points will go much more usefully in your other two souls, which is also where you get all of your attacks.
Many of the PvE souls have abilities that are very useful in PvP, and if you are very creative, I am sure you can create a perfectly valid PvP build without even using the PvP soul. Tanking specs have such high dodge/block/parry and damage debuffs that they offer immense survivability, healers, especially mixed with other soul types for survivability, are always useful as well. The Mage soul dedicated to CC actually has two cap skills that are strictly PvP. And of course, anything with a pet can kite the silly people who don't realize they should just kill the master and the pet will despawn.
Your Friendly Neighborhood Spec-builder, Ehli-san!
-~I'm not a strategist, I'm a tactician. Strategy is what you plan out ahead of time, tactics are what you do when you're in the thick, blades swinging and blood flowing. No strategist ever lives to become a hero.~-