[Xenakios]

IMHO GPUs have mostly been determined to be a disappointment for audio processing.

Yes, the power is there on the graphics cards, but getting the audio from the host CPU/memory into the card and back is an intensive process often involving long latencies. And latency is a poison for a great majority of people dealing with audio. It doesn't really matter if you could run 1000000 oscillators on a GPU if those oscillators sound noticeably late after pressing a key on a MIDI keyboard. Similar points would apply to things like guitar amp simulators and so on. GPUs might work passably well for some audio processing purposes where low latency isn't paramount.

Sometimes the latency could be reduced at the cost of increased CPU stress, but then that negates the idea of using the GPU to save on CPU resources...

You touched the issue of how would the things be programmed. There are ideas, languages and language extensions for it. Audio however is quite challenging because of the way the data has to be shuffled around in a particular order in order to do interesting things. GPUs are not fast because they have fast clock speeds. They are fast because they do parallel processing, and audio processing quite often is very badly suited for such processing. (There may not be enough actual parallel things to do in some given routing situation.)