While he goes into detail a lot more in that post and through several other posts on the forums, that small nugget of the planned changes in Cataclysm should already give us an idea of where they're headed. PvP is going to change. All healing specs -- not classes -- will gain defensive dispels against magic, the most common debuff type in the game. Most team compositions will have at least one member capable of removing magical debuffs and capable of dealing with almost all forms of crowd control. That's huge.
Of course, such a huge change comes with a price. As mentioned, all healing specs will be able to dispel magic through talents -- this means that paladin specs such as retribution and protection will lose their ability to remove magic, and all shamans will lose the ability to remove diseases and poisons. In addition, shadow priests will be unable to dispel diseases while in Shadowform. That has a profound effect on PvP. It changes the balance of things. Whereas shamans always had a handy solution to classes that used those debuff types such as rogues, hunters and death knights, they lose one of their trump cards against them.
In particular, Blizzard is removing Cleansing Totem from the game, as well as other spells that remove debuffs through pulses, such as Abolish Disease and Abolish Poison. The reasoning is that the devs want players to have an active role in dispelling debuffs, rather than having a pulse mechanic work it out for them. In the case of the previously mentioned spells, players simply fire and forget -- they cast the spell and don't necessarily worry about subsequent applications of debuffs. Some battle-hardened PvP players know how to actively dispel even when a debuff is applied, and this is the kind of behavior that Blizzard wants to encourage.
In fact, the developers want to penalize spamming dispels by allowing dispel abilities to consume mana even when there's no target. This means players will need to proactively dispel, which makes it imperative to have some form of alert when enemies gain buffs or friends are afflicted with debuffs. This could either mean the use of an addon or an improved interface with such alerts built in when Cataclysm finally ships. Players should start to wean themselves from the habit of spamming dispels "just in case" and learn to be more judicious in the use of such abilities. So while shamans appear to retain the use of Purge, spamming it against opponents without any buffs -- a common practice in today's PvP environment -- would be harmful to their mana pools.
The loss of magical dispels from protection and retribution is a massive blow to both specs in PvP, with Cleanse being a major component of their survivability. It is an extremely potent part of their arsenal, and it remains to be seen how Blizzard plans to compensate in terms of defensive capabilities, if at all. From what they've revealed so far, it seems as though Blizzard intends to keep defensive magical dispels within the healers' domain, although retribution and protection can still remove diseases and poisons. That said, they have become far more vulnerable, and Divine Shield (assuming it remains unchanged) becomes even more precious to those specs for clearing unwanted magical debuffs.
It's safe to assume that the schools of most classes' common sources of damage or debuffs will remain unchanged, that is to say that rogues will still use poison, death knights disease, warlocks curses, so on and so forth. The rock-paper-scissors nature of class match-ups got shaken up a little in this regard. For example, while shamans can no longer remove poisons and diseases, they do gain a baseline ability called Cleanse Spirit which removes curses, making them an even better counter to warlocks.
Zarhym noted that "when dispelling is trivial, either because it's too easy or because someone is capable of dispelling too many things, then neither PvE or PvP feel as strategic or tactical as we think they ideally could be," which also means that it is important to have a good mix of classes in a group. While pretty much all arena and battleground teams will be able to handle magical debuffs, there will be a school of magic that might give them trouble if they lack the proper class or spec. While a lot of things can still change from now until Cataclysm ships, it appears set that all healing classes will receive defensive magic dispels -- a much welcome change for PvP.
It's too early to tell exactly how much this will change the play style of specs and classes, but it seems that the changes are geared towards keeping DPS specs moving as offensively as possible in PvP. Enhancement and elemental shaman, for example, will only be able to remove curses by default, and yet curses seem to be dwindling in number. Curse of Agony, for example, will become Bane of Agony and no longer count as a curse, devaluing the ability in PvP.
Until we see the full list of changes that the devs have in store, we won't know for sure how things will pan out, but these changes along with the class previews seem rather positive. Blizzard has carefully taken different scenarios into account, going so far as to mention that shape-shifted druids might lose base immunity against Polymorph, preventing scenarios where Polymorph-immune healers can dispel the spell on their teammates.
The changes promote skill or proactive play. Players can no longer spam mindlessly without consequence. A lot of things will change, and the shake-up on dispel abilities is just the tip of the iceberg. Abilities are getting removed and new ones are replacing them. How does a Succubus that can knock back sound? A shaman casting the classic Warcraft spell, Earthquake? As the class changes slowly unveil, we'll soon get a better picture of how PvP looks in Cataclysm. From what we've seen so far, it's looking real pretty.