Norman Lebrecht has gotten himself involved in a discussion of how to pronounce "R." (Here for French, here for German.) This sounds like the sort of silly stuff I write about. My fanaticism is the pronunciation of the unpronounced neutral vowel in French. If it isn't pronounced, how are you supposed to tell how to pronounce it?
When native speakers speak both French and German, they often use a uvular or gutturalized R (back of the throat) instead of a rolled or flipped R (tip of the tongue). When I lived in Germany, my Spanish friend would laugh that she could do a guttural R only on the word "Brod." Then she would demonstrate. I couldn't do it on any word at all, so I was very impressed with this. My uvula refuses to do anything but just hang there. The fanatical German speech coaches fussed with a lot of things about my German but never once brought up how I pronounced R. Perhaps they simply assume that foreigners have no hope of achieving this. Or perhaps the uvular R isn't considered correct in opera singing.
I like to use certain models for these things. In French I think of Edith Piaf as the supreme model. Watching this again I can see her tongue rolling those R's. I am surprised by this.
For my money Régine Crespin and Edith Piaf are rolling with the tip of the tongue. This is what singers are taught. And you will please notice that neither one of these women use the silly super-rounded neutral vowel you are constantly hearing from coached non-French singers.
And Fritz Wunderlich is definitely using his tongue.
Christa Ludwig rolls with her tongue. The idea here is that you do nothing with your pronunciation that interferes with your tone because tone is king.
When the man in Brussels asks for a uvular R, he is trying for a theatrical effect. He wants Carmen to sound common. Here is a link to comments from the singer on this situation.
Curiously, if you go back a few posts to the film of Victoria de los Angeles, the word "chagrin" sounds the most likely to be guttural of anything I've found.
The only singer I am absolutely certain consistently uses a uvular R when singing is Gisela May.
At one point in the song she even sings it with her mouth wide open. No tongue. She was one of Brecht's favorites. We prefer to approach these subjects using the empirical method.