Sadly, my generation has no princess from their youth (the late 70s and early 80s were bereft of princess movies), but if you ask people (mainly women) of a certain age, they will tell you that either Ariel or Belle are 'their' princess. The kids who are between 7 and 12 right now will have Elsa and Anna. It will last. As a high school teacher, I have seen this quite a bit. A few years ago, there was a group of kids who all considered Mulan 'their' princess. Knowing I was a huge DW fanatic, they always asked me why there was no Mulan ride or even meet and greet. The kids now ask me the same questions about Tiana. The older middle schoolers are huge Rapunzel fans and I see a lot of frustration and resentment that Elsa and Anna has surpassed 'their' princess in popularity among the masses.
My point? The Frozen ride will live for a very long time. Today's 10 year old will be lining up for it in 30 years with their 10 year olds. Just like those a few years younger than I am are lining up for Enchanted Tales with Belle and Little Mermaid with their kids and the same way my parents took me when I was a kid on Peter Pan even though I had absolutely no interest in it. I learned to love the movie and ride and now my daughter goes on it with me and is learning to love the movie and the ride. I guarantee that for the next 30 years of Disney visits she will first force her parents (my wife and I) and later force her kids to ride a Frozen ride and eventually they will all love it.
Since it has been so financially successful, it has a LOT more people saying that Elsa and Anna are 'their' princess, which to Disney means it is worth the investment. Yup, Little Mermaid and Beauty and Beast had to wait 20 years for an attraction, but the dollar signs were blinking like crazy and the suits watching and for as small as the Maelstrom overlay is, it will definitely impact World Showcase attendance in a positive way and nothing will make them happier than big lines, news articles, and positive buzz.