If they were just doing something with the Motor Boat Cruise area, that wouldn't be so bad, but I have a feeling that the dark rides (at least either Mr. Toad or Pinocchio) may be impacted in some way by this if it does happen.
As it is, the Motor Boat Cruise alone is really too small to do anything with it, let alone anything "Frozen"-related. Here's a rough estimate of the footprint size (a little over 800 feet):
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Compare that with the space for the Frozen boat ride in Epcot, which is somewhat comparable and even a bit smaller than the Motor Boat Cruise area, but that doesn't take into account not just the People Mover track, but also those of the Monorail and Autopia:
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Frankly, I'm more worried about the Pinocchio ride being scrapped for a ride like this. Let's face it, it has scenes of tobacco and children-as-donkeys being sold off. It would give credence to the old rumor from Inside the Magic that the Pinocchio ride should be scrapped because of those.
What's more, I would say that between the upcoming overhaul of Splash Mountain and the ongoing overhaul of Toontown, Disneyland has plenty of stuff to keep itself busy without the need for "Frozen" stuff, especially if you throw Tomorrowland into the mix there.