I just ran into this today, I’m glad to know other people are thinking about it.
I think the subscribers set their own QoS so that they don’t have to wait for a message to be published before they can register their subscription on the DDS.
I’d really like to see clear warnings in rqt and rviz, at the moment they just silently drop image frames.
Docs regarding the design decisions behind QoS, and its usage would be fantastic.
Does anyone know of an example for QoS overrides at launch time?
edit: extra context for newcomers
https://index.ros.org/doc/ros2/Concepts/About-Quality-of-Service-Settings/