I have to agree. I really want to roll Horde (been playing alliance for 2+ years now). However, I don't want to start from square one on the Horde side and I'd like to be in contact with my (alliance) guild. So I don't roll Horde :(. Instead, I level my 4th 70.
I think breaking down the horde/alliance barrier would be great, even if limited to a player's account or guild.

You're correct. In pure story terms, the Horde and Alliance are not enemies, they are locked in a state of cold war as it were, with various hot spots, i.e. the battlegrounds. And if someone hits your city, you hit back, but apart from that they work together out of mutual need.

Neither the Horde nor Alliance possess the military power to defeat certain threats on their own. That was the concept of Warcraft 3, that's the concept of World of Warcraft, going all the way back to the AQ War. The Alliance and Horde are more often than not engaged in alliances of convenience, because they're too weak individually to defeat such monolithic and unilaterally evil entities such as the Burning Legion, the Silithid, The Scourge, the Blue Dragonflight, etc.

In Wrath you PvP people (WoW is a PvE game, first and foremost, PvP has always been an afterthought, admit it) will have a whole zone full of awesome new toys to play with. This is in addition to your precious arenas and battlegrounds.

There will be faction-specific reputations. There have been faction-specific reputations. There will CONTINUE TO BE faction-specific reputations, but what the author completely fails to understand, is that Blizzard doesn't care about what he thinks of the Alliance and Horde, only what THEY think of the Alliance and Horde, which is to say they have their differences and they do fight, often, but they are not idiots. Making WoW without neutral factions and sanctuaries would be ridiculous, would you rather the Alliance and Horde be pants-on-head retarded and get together before the AQ gates and beat the shit out of each others armies? Its about story, continuity, and common sense.

The factions have genuine differences that prevents them from being allies, so no, you will never see a "peace treaty" signed between them, you will see them cooperate toward a common goal against a greater enemy.