Well its clearly not vaporware because they have been actively testing the weapon system. We know this because they have confirmed both success and failures in the past. I believe the latest tests have been successful including demonstrating the full system from launch through glide phase to target hit.
The above quoted exchange during the House Armed Services Committee hearing seems to indicate the project is moving forward, otherwise they would have just said its been cancelled.
Furthermore, just because there have been problems with US solid rocket motor production base does not mean they cannot manufacture a rocket motor. They have numerous boosters available to them and launch missiles regularly.
