Thanks for the post, Jaime.
To add to your post, for an early introduction to unique network flows, please have a look at the design proposal here that is under discussion in the middleware working group.
Unique network flows between communicating nodes are essential for differentiated QoS from IP-based networks such as 5G. We at Ericsson are working on ROS2 interfaces that communicate to the RMW implementation that unique network flows are required. The intention is to make these interfaces generic enough such that any RMW implementation will be able to support them in a straight-forward manner.