I would imagine that if they had a new release to support that they would come back to the states.
The challenge for them touring in the U.S. is the fact that they have so many musicians and vocalist from different countries (Sia from Australia, Tina Dico from Denmark, Sophia Barker Henry Binns and Sam Hardaker (the core of Zero 7) are all Brits. Getting everyone, include the rest of the musicians together on one continent and getting through immigration hassels has been a challenge for Zero in the past. I do hope make it back the U.S. I would love to see them!