Not Kezan, because Kezan is home to more than just the Bilgewater Cartel, so more than 3/4's of the city would be neutral, not Horde.

I see Kezan as just an early starting zone (levels 1-5). Not sure though.

However... Bilgewater Harbor in Azshara could be your Capitol. I could see Her Tallest in that building with the Giganto-mongous cannon on top.

The key word here is "phasing", guys. At Blizzcon they said the new starting zones are going to use phasing extensively, like in Acherus. Please keep that in mind. I seriously don't understand why people keep thinking Gilneas is going to be a proper capital city, when everything Blizzard's told us so far has been to the absolute contrary. Barring some massive change down the pipe in the beta or something, neither Kezan nor Gilneas are going to be in the game as usable capitals past the starter levels. It's all phasing. The "Kezan" we're seeing is a tiny part of the island held by the smallest cartel (Undermine is the actual capital of the island, and it's underground), which is going to be evacuated because of the Cataclysm. Goblin PCs will be there probably all of 20 minutes, if that, depending on how long the phase of "pack up your stuff and get on the boats" lasts before they wash ashore on the Lost Isles. You could make an argument for the Bilgewater spot in Azshara, but that's not anything more than something tacked onto Orgrimmar's backyard. (Why build a complete capital city right next door to one? Makes no sense.) Blizzard's said a bunch of times now that Org's going to be the Goblins' city, and that Azshara's just going to be a low level goblin quest hub. The Autobahn they've got going just confirms that IMO. Think less Thunder Bluff and more Camp Whatever.

As for Gilneas, the same thing applies: phasing, phasing, and more phasing. We know the Forsaken are attacking it, and we know that Gilneas itself is going to be a Battleground. There has been absolutely nothing to suggest so far that Gilneas is going to be a capital city, why on earth would it be one if it's going to be a Battleground? The most likely probability based on the facts currently available points to freshly rolled Worgen starting in a heavily phased version of Gilneas, with the Forsaken stuff being introduced as the starting quests go on, and then the Worgen PCs hightailing it out into the wider world with no Gilneas to go back to unless they want to get some honor kills (other sections behind the wall might still be useable).

Obviously, it's still very early in development and anything could change. I'd personally love to see a part of Gilneas get reclaimed in a future patch, akin to the ruined part of Silvermoon vs. the capital part, or the Goblins build that harbor up into a proper city. But going by what we actually know right now, it's not very likely.