BTW, I’m not sure that rclcpp::Rate spins while it sleeps. It hasn’t in times gone by. Generally, you will break things in ROS2 if you sleep instead of spin; your buffers will overflow, etc. We usually use the timeouts on the spin methods instead.
The migration guide is a wiki page. Please feel free to edit it and improve it where you see fit. It would be good to post a link to the diff here afterwards to make others aware of your change. Thanks.