Comment # 1 on bug 905626 from Takashi Iwai

You'd better to report to PulseAudio upstream.  As distro we can't do much
things at all.

In theory, you can configure PulseAudio behaving like that, without dynamic
switching, by specifying the modules and options in default.pa explicitly.

Or, the virtual output sending all outputs might work.  But, again, please
report / ask upstream.  Thanks.