I still hear the word "fuss" all the time. And Ariel saying "Oh my gosh!" was pretty jarring to me even back then, and I still don't think it sounds normal or timeless. But Ariel became mute halfway through so that was fine. I only remember Rapunzel using "like" twice, both times while she was singing, but it was two times too much for me. Rapunzel already came across as modern from the way she acted and her inflections when she spoke, it just wasn't necessary to add 'freak out' and 'like' to her vocabulary just to hammer in the point OH LOOK SHE IS A BUBBLY CUTE TEENAGER YOU CAN TOTALLY HANG OUT WITH.I think what were modern quips back in the Snow White/Cinderella/Aurora eras are probably lost on modern audiences. "I'm so ashamed of the fuss I've made . . ." comes to mind. No one uses the word "fuss" these days but my grandmother and my wife's grandmother (who probably are the same age as Snow White would be) use it all the time (e.g., "Don't make a fuss over me".)
It's kind of like Ariel saying, "Oh my gosh! Have you ever seen anything so wonderful in your entirely life?" I was almost 16 when TLM came out so I'm about the same age as Ariel would be and when I was in high school, we said, "Oh my gosh!" all the time. But previously no princess had said anything like it. And now a days, it doesn't seem so hip/edgy because it's been part of the vernacular in American English for so long, it seems, well, normal.
I think what is "timeless" evolves over time. Rapunzel's excessive use of "like" may seem completely timeless by the time the film is 50 years old (imho, anyway)
I do agree that what is "timeless" evolves over time, but only up to a certain point. Modern language doesn't ruin the movie for me; I liked Tangled, LM, Frozen a lot, and Mulan is one of my favorite movies. But they feel just short of being a timeless classic or a masterpiece. I don't even think I'm that picky when it comes to modern quips either. The only things that really bugged me were obvious modern quotes like 'freak out' and 'like', and 'I don't do backstory' (wait, what? didn't even bother me much). I just think there are other ways to say things that don't sound as jarring.
However, not using modern language doesn't automatically make the movie a classic masterpiece either. Pocahontas would be an example of that.
I'm thinking especially when Scuttle clues her into how she missed the recital--"Oh. My. GOSH!!!--My father's gonna kill me!" 
