At ROSCon several people reminded me that they had expressed interest in helping with rviz and that I had dropped the ball on that (sorry!). Some of us at Open Robotics had gone so far as to write down some notes about maintaining rviz but got distracted before posted them. I finally finished that and put them in the GitHub wiki for rviz:
If you’re interested in helping with rviz maintenance I encourage you to open an issue on the rviz issue tracker (https://github.com/ros-visualization/rviz/issues/new) expressing that interest. I (and hopefully soon other maintainers) will communicate with you on that issue and either tell you next steps to becoming a maintainer or give you access to help with reviews and releases.
Maintaining rviz is not an easy task and so not for everyone, but if you have the skills and the time I think it can be very educational and a rewarding way to give back to the community.