[M] asks: "What do you think of Dawn Upshaw and Renée Fleming getting involved with high pop or contemporary opera?"
Of course, Dawn Upshaw is a contemporary music specialist. Her biggest early splash was in the recording of Henryk Górecki's Symphony 3 "Sorrowful Songs". This is a marvelous recording of a great work, both modern and accessable. It's a symphony in much the same way that "Das Lied von der Erde" is a symphony. Her appearance in the title role of The Cunning Little Vixen in San Francisco was quite nice. She rose to the challenge of playing a fox. Of course, Janáček is considered fairly mainstream these days. I have noticed that in the last decade or so his operas have become standard repertoire.
She is one of the "American singers" whose French I was complaining about. Dawn Upshaw reaches back only about as far as Debussy.
Renée Fleming used to be a pop singer. I would have to hear the pop efforts in question to have much of an opinion about them. I thought her "Over the Rainbow" was fun. It would depend on how she did it.
That said, it is generally the heavy singers who can't make the transition to pop. If they use an opera technique, it doesn't sound like pop singing at all. If they switch to a lighter technique, you wonder who they are. Renée and Dawn don't use such heavy technique in the operatic singing. I was somewhat put off by Renée Fleming's comments about using a microphone to allow herself to back off on her tone. That means she's intending technical differences.
The mistress of combining classical and pop was Eileen Farrell who was known to combine them on the same concert. Classical first, of course. The style changed significantly but the technique didn't.