Java 9 / OpenJDK 9 is planned for release this summer -- at the end of July to be exact. Therefore, Fedora developers are planning to get Java 9 into their release due out in H2'2017, Fedora 27.
But due to new APIs of Java 9, this updated in OpenJDK in Fedora 27 will just be offered as a technology preview. OpenJDK 8 will continue to be the default in Fedora until at least F28.
Java developers interested in the OpenJDK plans for Fedora can check out this Wiki page.
Among the new features coming to Java 9 are garbage collection improvements, HTTP 2.0 support, improvements to the process API, a jshell CLI utility, the new Jigsaw module system, reactive streams, a multi-resolution image API, TIFF image handling, the Java Applet API is being deprecated, and various other new APIs.