In an interview with The Boot, Kristian Bush said that Sugarland still has a contract to fulfill, so it's only a matter of time before fans get new music from them.
However, he has no idea when that will happen.
"The project's beginning time is really up to Jennifer. That's really [because of] the nature of how radio works: Her voice, as the lead singer of the band, is the voice that kind of defines it. And if she's working a solo project, it's very difficult, probably for a listener, to tell the difference [between a solo single and a Sugarland single]. So we as a band can't do anything until Jen decides to do it."
More here.