even Queen Elizabeth's christmas messages have become measurably less posh

To be clear, her reduced 'poshness' is due to changes in her pronunciation over the years, not the content or reading age required. She has moved to a more generic southern English accent rather than the 'cut glass' accent of the upper classes when she was born, in which 'house' would be pronounced 'hice' and 'trousers' as 'trizers'.