As we already know, ROS-2 is still under heavy development and there isn't a proper long-term release. Hence, writing nodes in ROS-2 directly or porting them to ROS-2 immediately would be an arduous task. There is an option where you could still use ROS-1 packages with ROS-2 packages to develop your projects. This is done through a package called ros1_bridge. 

It is actually an ROS-2 package, which establishes the automatic or manual mapping of messages, topics, and services and communicates between ROS-1 and ROS-2 nodes. It could subscribe to messages in a ROS version and then publish them in the other ROS version. This package comes in handy when you would like to use a simulator such as Gazebo with ROS-2 to test your project. There's only a limited number of messages supported in the ros1_bridge package at the time of writing. Hopefully, other packages will soon be ported into ROS-2 or their message support will be available in the preceding package so that we can run them in parallel.