Per-app sound mixer
It would be nice if you can add a volume mixer in the sound panel. Currently the sound panel looks like the following:

But it would be nice if we can change the sound intensity for different apps (in the sound panel or in the system settings) like in the program Pulse Audio Volume control as shown below.

I am also pretty sure this was available in elementary OS 0.4 so hopefully it will not be much of an inconvenience.
Thanks
I'm not sure this will be implemented - elementary design seems to be against per-app volume settings, as they were considered "confusing". For example this is the reason that both Music and Video players lack their volume widget/settings.
Attending a meeting/class and playing some music in the background is hardly achievable in elementary (music is louder than talk). I'm not sure if this kind of simplicity is what we need. Both google meet and the elementary music app have no volume slider so per-app sound mixer would be good.
For now I've made Mixer but would like to add this properly to elementary. My current thoughts are that with the new input and output selection, adding another row of items will make it very messy. Maybe this should be made into a separate indicator or in the sound plug? I'd love to hear thoughts
@danirabbit any thoughts on this? I have a few prototypes but I don't know what the desired location of this could be