We can do that already by recording a rosbag and then reading the data back on a laptop. Or by port forwading, changing rosmaster and blablabla.

This is just a quicker way to diagnose stuff. I do forest robotics, and when I'm in the woods with my robot the lesser fiddling with my laptop I have to do, the better. It's always great to be able to quickly verify that all sensors are working properly before starting an experiment.