I ignored this thread initially just because it seemed like the kind of thread that pops up every time a Disney movie is even mildly successful, but now that this rumor appears to be getting some traction on the internet...
http://www.broadwayworld.com/bwwmov...n-Heading-to-EPCOTs-Norway-Pavillion-20140103
...I have to join my voice into the choir that would call this extremely inappropriate and an absolute desecration of World Showcase's intent and meaning. This would be far worse than adding the Three Caballeros to Mexico IMO, as even Gran Fiesta Tour focuses on the real Mexico (albeit with cartoon characters), while I see a Frozen ride focusing on the real Norway unlikely.
All that said, I still have a hard time believing this rumor. This would be a much larger and more difficult change than Gran Fiesta Tour; Rio del Tiempo already featured screens as the main medium of the ride, and changing the films to include the Three Caballeros was a relatively easy change. Changes to the physical structure of the ride were generally few.
Maelstrom wouldn't be like that IMO. Full-bodied Animatronics, large physical set-pieces (unpopular as it is, removing that oil rig wouldn't be a small adjustment), and a turbulent ride system that wouldn't be very conducive to telling a story like Frozen. Changing Maelstrom would be theoretically possible, but I personally find it unlikely that Disney would commit so much to change a generally successful ride to a franchise that is still largely unproven in long-term popularity, especially when other Epcot attractions are in much greater need of attention.