I think gun-based CIWS systems had its day in the sun from 1980-2000's, but it's coming to an end. It replaced the old-style dual-xx mm AA gun systems that were incapable of intercepting sea-skimming missiles like the Gabriel/Scorpion, but is being rendered obsolete by missile based systems like RAM, ESSM, and (up coming) Sea Streak.
IMO we'll probably see navy ships with 2 x RAM launchers and 2 x remote-controlled small caliber AC. The small caliber AC will be less effective in CIWS role, and the primary CIWS system will be RAM or ESSM. To compensate for loss of 20mm-30mm CIWS guns, some navies will upgrade their ship's main gun to systems such as the Italian Davide or Strales system with DART guided munitions, for emergency use in CIWS role.
<img src="http://sitelife.aviationweek.com/ver1.0/Content/images/store/2/12/c20a82e8-76d3-4d7d-ac49-68c662a8ac7d.Large.jpg" alt="" />
Metal Storm is a neat concept, but will probably never make it to the deck of a navy ship. Faced with space/weight/cost constraints, designers will opt for missile CIWS over gun CIWS for better flexibility. A gun system must maintain lock-on target and can only intercept one target at a time, plus the Gatling guns will overheat very quickly. Missile based systems can intercept many more targets at once, and the latest missiles have "lock on after launch" for fire-and-forget interception capability.
Here's an article from Zhuhai 2008 air show's FL-3000N product, basically the Chinese defense industry came to the same conclusion and is emulating US/German RAM concept:
<img src="http://www.centurychina.com/plaboard/uploads/FL-3000_RAM2.jpg" alt="" />
