Reading Wuthering Heights at the moment, and the dialect is nothing if not striking:
“‘It’s noan Nelly!’ answered Joseph. ‘I sudn’t shift for Nelly—nasty ill nowt as shoo is. Thank God! Shoo cannot stale t’ sowl o’ nob’dy! Shoo wer niver soa handsome, but what a body mud look at her ’bout winking. It’s yon flaysome, graceless quean, that’s witched our lad, wi’ her bold een and her forrard ways—till—Nay! it fair brusts my heart! He’s forgotten all I’ve done for him, and made on him, and goan and riven up a whole row o’ t’ grandest currant-trees i’ t’ garden!”
Presumably television and YouTube will continue the erosion to the point where in a hundred years or so dialect will be detectable if at all only in the finest nuances, other than which we will all speak a pretty much homogeneous tongue – a magnolia blend of BBC/Home Counties and imported American with just a soupçon of estuary.
(“her bold een”….I seem to remember ‘een’ as a plural for ‘eye’ from my days studying Chaucer. So over the course of a millennium, presumably, it has retreated steadily from the language of the land to a few remaining redoubts, until one final demise made it history, never to be seen or heard of again…other than on the screen of a thousand students’ Kindles.)