This issue doesn't seem unique to Swarm; rather, it is a generic request for the Sonar plugin to push metrics to SonarQube from the agent to the master through JNLP and then from the master to SonarQube through TCP. This is definitely not a Swarm issue; rather, it would apply to any form of Jenkins agent (including SSH Build Agents). While it might be technically possible to implement such a system at the Remoting layer, I doubt the Remoting maintainer(s) would want to add SSH-like tunneling support to Remoting merely to satisfy this use case from 9 years ago. Nevertheless, if you feel strongly about this, please open an issue against the "Remoting" component to see if the Remoting maintainer(s) are interested in pursuing this further.
KK does not maintain this plugin anymore. Moving to unassigned to set the expectation