Within this thread, I would like to focus on the first issue.
- Bring the license information into the packages for ROS1
Totally fine for me. Then, I think you are pretty much set already:
The easy way would be to create an issue and a belonging pull request to add the license info file for each package.
This is the go-to option. Everything else seems overkill or too complicated. I’d also suggest to only target melodic and noetic dev branches and ignore the rest.
At least it would be helpful if the package maintainers are informed about such a change. And if the approach is agreed by the quality assurance group.
This is vital in getting any traction. Involve OSRF and the quality assurance group. They need to be on board. The rest of the maintainers might much more easily follow once this is set up for the ROS core packages…
If you can get this to land in ros/ros and ros/ros_comm, I’d already consider this a success. The rest would then “only” be replication of whatever happend to those repos (granted, much work and probably quite a few discussions).
You should probably present this (one of) the next Quality Assurance Working Group Meetings. Next happens to be on October 1st 
October Quality Assurance Meeting Thursday, October 1st 2020 
Would be much appreciated, but I guess you should talk to the OSRF/QA-Working Group first…