The DD-21 Zumwalts with their 6-inch guns, which may eventually be replaced by mass drivers, seem analogous.
It will be a few years before the Zumwalt class is online.
The gun is going to be 155mm (close to 6") for the "Joint"
classification of the projectiles. The 8" gun originally
designed for the Spruance is still sitting at Dam Neck.
The cargo projectiles be used in the 155mm round are
more efficent killers that the massive 16" projectile.
http://www.vectorsite.net/twbombb.html