There was an interesting article in the Guardian last month about whether the Glasgow dialect was being eroded owing to the influence of television and modern life. As with all such popular expositions of detailed academic research, in this case that of Jane Stuart-Smith, it runs the risk of raising more questions than it answers.
However, one of the key points seems to be that the partial loss of rhoticity in Glaswegian is, far from a new development, a remarkably old — and therefore rather stable — feature of the dialect. The main contributor is the emergence of a pharyngealised /r/, presumably owing to glottalisation of a preceding /t/, although another, even older feature is assimilation of /r/ in words such as "further". Such assimilation is also recorded in Ulster (Robinson's 1997 grammar lists the form thie for "three"). According to Stuart-Smith, there is even partial loss of rhoticity in a 1916 Wilhelm Doegen recording of a Scots POW.
Of course, those familiar with Duncan Macrae reciting "The Wee Cock Sparra" ("tho he wasne his farra") might have been somewhat sceptical of the hypothesis about a sudden erosion of Glaswegian rhoticity in the first place. Why it has not led to a much more thoroughgoing loss is anyone's guess, but it may be to do with the fact that the phenomenon only happens in one of the (linked) registers available to residents of the city.
A much more dramatic erosion, however, is mentioned only obliquely, as if it were understandably of lesser interest.
"You can hear how he uses lots of Scots vocabulary, but if you listen very carefully, you will also hear that he has almost no "r" sounds in some words like "father"."Clicking the link reveals a recording of the story of the Prodigal Son, read fluently in traditional Scots (the word turns out to be "faither"). A note on the speaker states: "His mother tongue is Scottish, views his learning of English as an 'additional language'." The Blether Region is unsure which version is being read; it is not William Wye Smith. It may be a Bonaparte translation, or the speaker's own.
One wonders how many Glasgow people would be able to reproduce the Doegen recording today. Certainly not all.