All other apps on my system are already using gstreamer 1.x,
(Parole, Xfce's recommended media player, also uses gstreamer 1.x),
only xfce4-mixer still requires gstremaer 0.1x.
Could xfce4-mixer please be ported to gstreamer 1.x ?
Just add a couple of things.
+1 going to gstreamer 1.0, due that officially announced that do not will maintain this version, and not even accept bugs.
The problem is that it is impossible to port the mixer to gstremaer 1.0, because the interface gstmixer that uses xfce4-mixer was not ported to gstreamer1.0, and not write any replacement (Now not found the official announcement).
In this situation we must return to using the old code, re-using alsa-lib and OSS4, or go directly to pulseaudio as gnome , or other more multiplatform approach as volumeicon 
I think xfce should go back and use alsa directly
(and perhaps alternatively oss, but that's very dead, isn't it?).
pulseaudio is against xfce's goals of being small,
and is not present on many systems, especially small ones.
And alsa and oss have very stable interfaces,
whereas pulseaudio is a moving target.
I was playing around with libgvc (Gnome Volume control), but it is highly dependent on pulseaudio.
There are now an interesting option. libmatemixer, that according to the readme file:
> libmatemixer is a mixer library for MATE desktop.
> It provides an abstract API allowing access to mixer functionality available
> in the PulseAudio, ALSA and OSS sound systems.
Both alsa, oss (No oss4) and pulseaudio seems well maintained.
What do you think? Is it a good option?
This week start to test it om my xfce4-soundmenu-plugin, and if it offers good results, can try to porting xfce4-mixer.
p,s: Please comment everybody. It will require work and I have not much time. I not want to work hard and be useless.. haha.. ;)
libmatemixer currently seems to be the best (only?) alternative.
They had exactly the same problem in Mate, and they solved it.
Consider xfce4-mixer dead. For those with PulseAudio, look into xfce4-pulseaudio-plugin. Otherwise, perhaps libmatemixer or maybe there's something else. Either way, xfce4-mixer will not be ported to gstreamer-1.x according to its maintainer.