It's currently used for military radar but NTIA is looking to make it available. The work around CBRS is proving that sharing spectrum can work, even if the military is an interested party. Before using the band, you would have to check with a database to see whether it isn't reserved.
The classic example is naval shipboard radars. A user in Iowa is unlikely to cause interference. Research in the 3550 CBRS band finds most of the U.S. is not in use. It would be natural to simply expand CBRS down another 100 MHz.
The primary source is a blog by David Redl at NTIA, below.