Warlocks get a playstyle overhaul as well, with the new soul shard mechanic that acts a spell booster. Using Soulburn will use up one of three soul shards and empower a few spells and grant them a special effect. Soul shards do not generally regenerate in combat. For the first two battleground brackets, expect warlocks to use Soulburn to achieve the following effects: summon a demon instantly, reduce the cast speed of Drain Life, allow Healthstones to increase health by 20% for 8 seconds, get automatic crits for Searing Pain, and affliction warlocks can use it to detonate Unstable Affliction. This list of abilities and secondary effects are still in flux, but the idea is that warlocks get a lot of utility from the soul shard mechanic, even at lower brackets.
Because life spans in battlegrounds are pretty short, expect warlocks to use Soulburn more often than normal in an effort to expend all soul shards before taking the next trip to the graveyard. This means a huge playstyle change for warlocks in battlegrounds -- a marked difference from boss encounters where they're likely to be conserving their soul shards for optimal DPS or even arenas where they need perfect prudence in burning up their limited resource. There's the threat of it becoming an imbalanced mechanic in the battleground environment, but it remains to be seen how the developers pace soul shard recovery.
Affliction - As mentioned, affliction warlocks get the excellent PvP spell Unstable Affliction at level 10. Although there are far fewer magical dispels at lower levels, the secondary effect should come in handy. Affliction warlocks have excellent health recovery with Soul Siphon (especially when burning a shard to expedite Drain Life) and Siphon Life. The downside is that affliction warlocks get their complementary Felhound pet one level past the lower level brackets.
Demonology - On the other hand, demonology warlocks get their big, burly bodyguards right out the gate. Although the developers are currently exploring the option to make Soul Link baseline, it's currently exclusive to demonology warlocks and should be available from the 20-29 bracket onwards. There's little by way of pet killing on the battlegrounds as compared to arenas, so talents such as Fel Synergy and Master Summoner are devalued, especially at lower levels.
Destruction - Destro locks get Conflagrate but the more interesting mechanics and talents lie deeper in the tree, such as uses for Soul Fire and soul shard refund through Shadowburn, which becomes available at level 30 in the current beta. Destruction warlocks seem much more squishy at these levels than either of the other two specs, and consequently unlikely to be popular in these brackets.
Arms - I don't think players can get any more excited about Mortal Strike coming in at level 10. With healers getting a formidable complement of heals at low levels, Mortal Strike comes in handy to balance it out. Passive rage regeneration and more rage generated mean that arms warriors can dish out a lot of damage. The first two tiers of the current arms tree give warriors a few good PvP talents such as Blitz, Second Wind, and even Field Dressing. In the case of the latter -- bandages will come in pretty handy.
Fury - Fortunately for everyone else, fury warriors don't get Field Dressing until much later, so Bloodthirst won't benefit from it in the lower level brackets. Unfortunately, fury warriors also get Blood Craze on the first tier to compensate. This means a lot of passive self-healing going on through an offense. Fury warriors also get the PvP favorite Piercing Howl.
Protection - Tanks get Shield Slam, but the more exciting PvP-viable talents and abilities come much later. This means that the biggest benefit players can get from PvPing in protection spec are the basic tank bonuses such as more stamina and better defense against melee. At these levels, protection warriors are actually the strongest against melee
Low level fun
Low level PvP seems set to be incredibly fun, mostly because the battlefield will be incredibly diverse. In the current environment, most classes start out pretty homogeneously, with one or two specs being preferred for PvP due to the availability of key PvP talents. In the new environment, most specs should be well-represented as it will come down more to preferred playstyle rather than purely what is optimal or imbalanced.
Of course, part of what should make low level PvP exciting is the gear. The developers have a chance to create new low level items with the resilience stat, as well as make distinctive armor and weapons for low levels. In the current beta, there are newly designed gear that come from quests that look very good compared to the hodge-podge designs from when the game was new. If you choose the right rewards from quests, you'll emerge from the starting area looking rather spiffy -- a lesson developers learned from the death knight starting area in Wrath.
Hopefully, the developers do something similar with low level PvP gear. With a new honor and conquest reward system in place, players should have access to gear that feels rewarding. Early on, there should be a distinction between PvP and PvE items, further reinforcing the different feel of both playstyles. Given that the devs have shown care to redesigning low level gear, let's hope they pay as much attention to PvP itemization. It should go a long way towards encouraging new and leveling players to try out PvP.
The new system is exciting because any player regardless of spec will feel that they have something to contribute on the battlefield. At low levels, it's also not quite necessary to have a 'PvP spec' and most of the talent choices will be useful for both leveling and in the battlegrounds. There will be much more variety in terms of playstyles and strategies even in the lower brackets. The new specialization system should make low level PvP in Cataclysm the most fun it has ever been. All it takes is a little push and a few more incentives in the game to have all the players going at it full bore. But here's the kicker -- as fun as everything will be at lower levels, imagine how it's going to be at level 85, once players finally unlock all the possible abilities and skills. It's going to be pretty crazy.