As we iterate on the ROS release schedule with ROS 2, I’ve started a proposal for how a rolling ROS 2 distribution might work. Please take a look at the draft of REP-2002 and give it your feedback: REP 2002: adding a rolling ROS distribution by nuclearsandwich · Pull Request #209 · ros-infrastructure/rep · GitHub.
PS, you can view the latest state of the draft REP rendered on GitHub with this link.