This is a prime example of the hyperbole created when nostalgia, romantic notions of what never was, and the irrationality of not accepting what is clearly in high public demand and shows no signs of slowing down.
* "Characters don't belong in Epcot!" - Characters have been a part of Epcot since it opened, I can show you pictures of me with Space Minnie from the 80's, and pictures of meeting the World Showcase double-decker "Character Bus" that used to bring them out there (I believe Chip and Dale used to run with that crowd).
* There is no "slippery slope" here as is being implied - unless Disney is suddenly going to spend the money and build attractions at more countries, this was it folks. And you know what? If Disney does want to build more attractions - heck, since they build so few, at least they would be building something, LOL. That said, I do not for one second think you have to worry - the rest of WS will remain as stagnant as it has been for the last quarter century for your continued shopping and substance consumption enjoyment.
* The ride everyone is kvetching about replacing was ALREADY seen by many long-time observers as the first shot in the "ruination" of the edutainment aspect of Epcot to begin with. There is nothing educational nor specifically historical about it - a ride largely of darkness with some brief show scenes with references to esoteric Gods and encounters with mythical Trolls, and suddenly an oil rig is involved. At least now folks will know what the bloody heck is going on in the attraction and it will have some cohesiveness.
This is coming from someone who is only a theme park fan because of dark rides, and I've always had a soft spot for Maelstrom in particular because of it's quirky nature - but as I said before, blindfold someone, bring them to the ride vehicle, remove the blindfold, and let them ride - if you asked them when they got off maybe 1 out of a 100 would have said "oh, Norway!" That's why they have that tacky film at the end (which for the past decade has been the only thing anyone has ever discussed about the attraction - more specifically - how to get around watching it).
I can't speak for the fans of the film. I'm not one, at least yet (though I do quite like Kristin Bell). Truth be told, haven't even seen it (though I'm thinking I might finally do so this weekend, this has all piqued my interest). Yet, I know all the characters names, the plot, the songs - because it's so popular and has struck such a chord with audiences.
That said, you just told the story of every attraction pretty much ever. Yes, it would be great if Disney built a big castle in Fantasyland and put a great dark ride in there. Oh wait, they did that with TLM - but some folks around these parts consider that a failure.
I don't think this is perfect, nor the best thing that could have happened - the point is, a lot more folks are going to be pleased and excited about a Frozen attraction than ever were about the confusing juxtaposition of elements that is the Maelstrom, as much as I enjoy quirky dark rides. This does nothing to change WS except give it an attraction that folks actually will want to seek out - but like I said, don't worry - the rest of it will remain the stagnant museum with the revolving door of restaurants that it always has been, Frozen isn't going to change that.