in an absurdely late / early morning Twitcan session, Zayn apparently confirmed the boys ARE going to the US in January!
this means that Simon Cowell is very serious about trying to break the boys in America. I suspect they'll visit either Los Angeles, New York, Miami o Atlanta - o all four! Those are the places Cowell took Leona Lewis to work on her album. Those cities are where all the major US song writers and producers live and work.
I suggest 1D fan keep a close watch on Twitter as many songwriters and producers have Twitter accounts and quite often like to tweet about who they're working with and sometimes Tweet pictures.
Although I have a feeling the boys won't be able to contain their excitement and will probably tweet up a storm themselves.