Interesting, but I've found no official references to Melroy or Caldwell's assignments to STS-119. Unless I've missed something, there's nothing on either of their bios which refers to STS-119, nor any recent NASA press releases.
I also heard some time ago that Halsell, like Wilcutt, had chosen to step down from their pre-107 commands to give others a chance to fly. Also, I understand that Ken Bowersox (the Director of Flight Crew Ops) made an announcement a couple of months ago that more-or-less says four flights is the limit. Wilcutt, Parazynski and Gernhardt have already made four and Halsell has five under his belt.
A link, or press release, for the Melroy-Caldwell-Halsell assignments would be much appreciated, as would any comments about the others. Can anyone help?