I think it's a given that Series Four won't be as British as the first three series, but I don't necessarily think that's a bad thing. RTD's work on Doctor Who and Torchwood have always been about, amongst other things, British patriotism -- appreciating British culture and history, appreciating the diversity that exists within the United Kingdom, celebrating the accomplishments of Britons throughout history, and examining the behavior of the British government.
And here and there throughout his work, there have been hints about the relationship between the United States and the United Kingdom. Much of it has wobbled between appreciation and skepticism or even rivalry -- Captain Jack is clearly based upon the archetypes of American action heroes and he's generally seen in a positive light, America was depicted as having every intention to send vital humanitarian aide to Britain after the London detonation in "Turn Left" before being devastated by its own national mass murder, and certainly Barack Obama was depicted in a positive light in "The End of Time, Part One."
But, on the other hand, you also have the "He's not my boss" bit from "The Christmas Invasion," the U.S. President-elect being depicted as a jackass for taking control of first contact with the Toclafane away from the British (and for putting the U.S. seal of office on the related documents and broadcasts rather than the U.N. seal, even though the Valiant was a U.N.I.T. vessel), the reference to a future war between Europe and America in "Voyage of the Damned," and the overbearing American military seizing control of the British government in the final episodes of Children of Earth.
So what I'm looking forward to -- and what I think will be interesting, with American writers aboard -- is seeing The New World explore more of the relationship between Britain and America in the Whoniverse. Is America a friend or foe, heroic or villainous, as embodied in the relationship between the C.I.A. and Torchwood? The C.I.A., of course, has been involved in a lot of shady stuff throughout its history and isn't necessarily a good reflection of America overall -- but then, that's true of the Torchwood Institute, which of course was depicted as an antagonist of the Doctor's throughout Series Two.
So, yeah, The New World won't be quite as British, but I think that by examining the relationship between the United States and the United Kingdom, that may be a good thing. Being less British doesn't mean that it will be Americanized.
ETA:
He's probably busy with Law & Order: U.K. RTD is bringing a British show to America, and Chibnall is bringing an American show to Britain! Isn't syncretism fun?
