Young Frankenstein...I think you could make this movie, but there's no one in Hollywood that could play Marty Feldman's Igor.
Blazing Saddles...It's often cited as an outright dare to censors but really it's a very special episode. The most important line in it is "Ah prairie shit. Everybody!"
History of the World Part 1: The naked homophobia in the Caesar's Palace sequence isn't going to work in the 21st century. I think you could make The Musical Inquisition starring a singing dancing Torquemada but it would still have to be played by a prominent Jewish comedian. And from the French part of the movie, I think the main thing they'd cut is the old man freeing all his dead birds.
Spaceballs: no notes? Modern Hollywood wouldn't greenlight this movie because they can't sell parodies in China.
Robin Hood: Men In Tights: I'm not sure how "Testicles of a newt. Guess he's a transsexual now!" would fly in 2024. Can I share something strange? I 100% believe modern Hollywood would be able to make Robin Hood Prince of Thieves complete with the scene where Alan Rickman forces Mary Elisabeth's legs apart with his feet, but I don't think they'd be okay with making a lighthearted parody of that same scene where he uses an anachronistic jackhammer on an Everlast brand chastity belt.
I had a great idea for a movie a while back, a bunch of guys in their 50s trying to relive their youth by doing classic "pranks" from the movies from their youth and figuring out half way through that they were committing sex crimes and felonies and then hilarious hijinks ensue as they try to unravel their idiocy.