A Guide Through The Linux Sound API Jungle

However - weighing the work required to create Phonon and its backends vs the potential work needed to maintain gst 0.10 for a while on your own (there will likely be other organisations interested in a stable 0.10 branch too however) if a gst were to happen during 4.xx, I'd probably avoid building something completely new.

However, this is a judgment call, and I trust you have a lot more experience with it than me. You address the problems with supporting 0.10 yourselves in your mail from 2 years ago:

"So if we just rely on gstreamer 0.10, now we're stuck with an abandoned code base, which KDE developers are unfamiliar with. Does this sound familiar to anyone? ;)"

I think this is the crux of the issue.

You've avoided this by creating Phonon. However, I believe 0.10 has quite a bit of mindshare, and I believe that the KDE people would not have found themselves all alone maintaining the abandoned 0.10 (while OTOH they are pretty much on their own maintaining Phonon). Well, I do see how this might seem very similar to the aRts situation, but aRts wasn't used a lot outside of the KDE world. Maintaining Phonon + backends (which have to interface with the codebases you're not familiar with) must take quite a lot of effort too.