The AQI (Australian Quesioning Intonation) has been a linguistic marker used to track language development for the last 20 odd years (I know, cos I wrote an essay on it once
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The other linguistic oddity that was mapped in the same way was the "non-prevocalic r" - the over pronunciation of an r in words (a bit like what we might think of as the English South West burr) that was perceived to be more prevalent in the upper-middle classes in 1950s America, so it was forcibly adopted into aspirant working class accents.
There is also a feminist paper that argues that the AQI has increased in frequency as women have become more powerful and successful as it is a "femine" softening of a statement - make it seem like you are asking a question/seem unsure, when in fact you are giving a straight instruction, for example. Don't know how much I subscribe to that idea.