Did prescriptivists make up pied-piping in relative infinitive constructions?
A quick Internet search suggests that pied-piping in relative clauses was a natural feature of English even though it is loved by prescriptivists; it existed in older stages of the language, and it was declining by the 17th century, but it was preferred by some prescriptivists and survived into the modern times.
What is the history of pied-piping in relative infinitive constructions as in the phrase a room in which to read books? Was it actually more common (or obligatory) in the past as in relative clauses, or did prescriptivists make it up, thinking that the grammar of English should be like that of Latin?
"Pied piping" is a term used descriptively by linguists to describe certain relative expressions containing more than just a question word. I am unaware of any connection to prescriptivism. However, there could be some influence from Latin. The term itself is due to Robin Lakoff, whose dissertation was on Latin syntax.