Can we expect canberra to be available everywhere PA is?

It seems that it's just playing a short ticking sound, perhaps we can avoid the dependency easily?

Is the feedback only played when there is no other source playing?
If not, it should be done like that. If you already have something playing, it's just annoying to play an additional sound, and does not provide any additional info because you notice how loud whatever is playing plays.

Can we expect canberra to be available everywhere PA is?

KF5 kmix has it as non-optional dependency too, so I think that should not be issue.

Is the feedback only played when there is no other source playing?

It's played even if there is something playing. It uses the notification sounds event type, so if the user has it muted there will be no volume feedback sound even when enabled.
Also it is not trivial to detect if there is nothing playing, user may have for example some app that sets very low volume for its stream, or even there may be stream that is playing silence.

In D2219#42870, @colomar wrote:

Is the feedback only played when there is no other source playing?
If not, it should be done like that. If you already have something playing, it's just annoying to play an additional sound, and does not provide any additional info because you notice how loud whatever is playing plays.

I don't think it's technically feasible to detect if something else is playing. In general, I agree, but once you look closer, it's really complicated, too complicated, in fact.