Starting with the release of SAP GUI for Java 7.50 rev 5, there is a big change under the hood. While depending for almost two decades  on the Sun and later Oracle JDKs to run SAP GUI for Java, big efforts have made it possible to run SAP GUI for Java now also on OpenJDK 11 and OpenJFX 11.
Why that out of a sudden?
Before Java SE 11, the OracleJDK came with JavaFX bundled in the installation package. After Oracle has decided to decouple JavaFX from the JDK and make it a separate open source project named OpenJFX , targeting OpenJDK has become more attractive for SAP GUI for Java. JavaFX is the UI framework that provides the functionality of a web browser component used by the browser control in SAP GUI for Java for rendering html content.
In addition, facing the end of Java 8 public updates by January 2019 , it obviously became necessary to move on to a newer version of Java SE.
With Oracle’s changes to its Java roadmap  and licensing , using OpenJDK 11 is the preferred way to go. It is an LTS release (long term support) and comes with a "GNU General Public License v2, with the Classpath Exception (GPLv2+CPE)" also for commercial use . In contrary, the OracleJDK requires a subscription for licensing and support for commercial use .
With SapMachine, SAP offers its own downstream version of the OpenJDK project. It is a SAP supported version of OpenJDK for SAP customers and partners who wish to use OpenJDK to run their applications .
The new foundation to run SAP GUI for Java is SapMachine 11 and OpenJFX 11 .
Why is this bold move in the middle of the lifetime of a SAP GUI for Java version and does this jeopardize stability?
It has been almost impossible to sync our schedule with the Java roadmap since latter has been changed again and again in the last few years. Java 9 was too late for SAP GUI for Java 7.50 and both Java 9 and 10 figured out to be short term releases with a lifetime of six months only. Only recently, the Java roadmap seems to have stabilized and with Java 11, a Java version with a reasonable lifetime became available. Development of the next major release of SAP GUI for Java is still ongoing, so it couldn’t have been made available in time once Java 8 is no longer publicly supported.
However, most of the changes and renovations in the codebase of SAP GUI for Java 7.50 required to be able to run on Java 11 have already been made early in the development cycle. Only the installer and initial startup process have been extended recently to be able to handle both Java 8 and Java 11. Several person months have been spent with testing on all three platforms and their findings have been addressed. So we expect no negative impact in regards of stability.
There are two options after the end of public updates of Java 8 in January 2019:
Still using SAP GUI for Java 7.50 running on Java 8 with a Java SE Subscription  to have continuous access to updates or to migrate to SapMachine 11 and OpenJFX 11 in time. For latter please download the new version and read the documentation for installation instructions part of the manual and locations for downloading SapMachine 11 and OpenJFX 11  .
For feedback and questions, please start a new post. In case you find issues, preferably create a support message on component BC-FES-JAV.
Thanks to all who contributed to make this happen: the Oracle Java team, the OpenJDK and OpenJFX projects, the SAP VM and SAP GUI for Java development teams and all the testers in quality assurance.
 The first public beta of SAP GUI for Java was published on Dec 6, 1999. Happy Birthday!