"This single, relatively homogeneous dialect will be noticeable with the first generation of children born on the space vehicle and will surely result in a dialect that differs from all the parents' dialect, and from every other dialect of English spoken on Earth," Thomason said.
(via Plastic)
This seems more to be a sociological issue than lingustics. The premise seems to be that the complete physical isolation from earth, combined with constant exposure to a small population would cause new generations to deliberatly try to seperate themselves from their heritage.
But what, other than sex, are people going to do for entertainment. We have hundreds of years worth of literature, a hundred years of films, and many decades of recorded music. Plus reams and reams of educational material that will be necessary to educate spacefaring children in the skills necessary to keep the spacecraft running. Send those along, and it will be a massive break against the dialect changing so dramatically that they would be unintelligable to earth bound humans upon their return.
In any case, I would be first in line to sign up for such a mission.