I was also referring only to a switching supply in an AB environment. The problem is that even at 150K, I have found noise components at audible frequencies due to beat frequencies, bad filtering (ringing) etc. It also introduces harmonics on the grounds which permeate the entire system, resulting in a general high energy noisy environment, which can show up at the outputs as white noise.
I'm not saying it can't be done, just it would be very difficult to get the kind of performance a home user would demand. In my opinion I think thats why class G was created, to give some efficiency with a reasonable noise expectation.