A truck carrying new 2015 Subaru WRX STIs was spotted by a local fan in Omaha and shared on the Subaru Enthusiasts (Nebraska) Facebook page. It's likely that these cars are on their way to a pre-launch event for Subaru. Because the cars weren't covered, as they would be for delivery to a dealer for stock, they are probably used for the reviews that have been suddenly popping up on sites like DrivingSports, Jalopnik, and other notable sources. They're also being used for Ride-and-Drive and Breakaway events that are held for training and education for local dealerships.
Ordering for the new WRX and WRX STI opened up last week, so a late-March/early-April release seems imminent. I will be attending the Breakaway event on April 9th for the '15 WRX and WRX STI, so I'm curious to see if the cars reach dealerships in my area before then.