Thanks for the suggestion. For those of you who haven’t seen it @BrannonKing put together a PR for the ROS2 Time design document.
If you’re interested in this topic I’ve replied in detail at: https://github.com/ros2/design/pull/128#pullrequestreview-35463951
At a high level I don’t think that we want to overload the simulation /clock abstraction to support system time synchronization as well. Clock synchronization is something that is quite specialized and there are many mature mechanisms for doing that already. We don’t want to have to provide our own implementation when we can leverage existing technologies such as Network Time Protocol.
For the use case of a system that starts without a system clock. It’s relatively straight forward to have it run ntpdate or chrony on startup to get it to the right system time.