For years, the scuttlebutt has been that Catastrophe Canyon is being torn out and the new Pixarland will go into that area. They have already done the dryrun for this in Disney Studios Paris, and unless they make huge changes to it, I don't see it coming to DHS in the near future. The rides are interesting and eye-catching -- they are also extremely low capacity with 70-90 minute waits even on empty park days. Unless they seriously rethink the whole thing, I don't see this coming to pass anytime soon.
This particular closing is most likely just plain old maintenance -- a bit of paint, repairs on the trams themselves (they have multiple breakdowns a day), repair of the water cannons that don't work in the tank, etc. I wouldn't expect any changes to the Pearl Harbor themeing, nor anything else.