Probably just a rumor. I doubt they'd change a long standing icon of WDW and Disney in general. Could a Frozen castle or the town be built at some point? Yeah, I could see that, they did it with Beauty and the Beast and it's pretty cool (though, maybe due to being from the northeast, when I'm in Florida I'd like to keep the snow to a minimum, unless it's the fake snow they blow around during the Christmas party events).
Also, they have the castle show, which wasn't bad, it was kind of a cool crossover and they have the lights on the castle anyway, so it worked out well and it's kind of cool the castle is being used more diversely now.