There were a couple of additional pieces of information as well.
- Other Coast Guard vessels will also get the Mod4.
- There are no plans to replace existing 25mm mounts with the 30mm Mod4.
The answer on the Polar Security Cutters is probably definitive because it is still three years in the future. Presumably the Navy will use up the 25mm mounts they have already purchased before installing the Mod4. The Offshore Patrol Cutter program extends so far into the future, it is likely most of them will receive the 30mm.
I would argue, vessels for which the Mk38 is the primary armament, particularly if they have only one, should receive a higher priority for the more capable Mod4 since we know the 30mm is more effective than the 25mm, and these vessels have no more powerful alternative weapon they could employ. It appears the WMEC270 that are going through the service life extension program fall in this category.
As for upgrading existing installations, there is a strong case to be made for upgrading the PATFORSWA Webber class WPCs. The 30mm offers options that are not available for the 25mm including an airburst round that can be used against UAVs and a swimmer round that is particularly effective against swarming fast inshore attack craft, both significant threats in the Persian Gulf.
The post also refers to the possibility of mounting missiles on the mount. That possibility was discussed in more detail here. I would like to see all the 25mm guns replaced by the 30mm, but if the earlier Mk38 Mod2/3 mounts were modified to mount APKWS guided rockets or Hellfire and its successor, there would be less need for the larger caliber gun.