No, you need to go way way out of your way to make a real world example for that - otherwise it would have been discovered by a bug, not by academics. It’s similar to Java’s generics being Turing complete - cool, but you can never make use of that/write it accidentally.
I am not as inclined as you to think that accidentally creating an unsound type system is no big deal. Soundness is exactly the property that makes type systems useful. Note the adverb at the beginning of the paper’s abstract:
> Fortunately, parametric polymorphism was not integrated into the Java Virtual Machine (JVM), so these examples do not demonstrate any unsoundness of the JVM.
No, you need to go way way out of your way to make a real world example for that - otherwise it would have been discovered by a bug, not by academics. It’s similar to Java’s generics being Turing complete - cool, but you can never make use of that/write it accidentally.