Let’s see. Was on JFocus19 in Stockholm, and from Oracle this is how I understand it will be.
Java is developed in/by OpenJDK, which is not Oracle. It has a release schedule of 6 month, and that is not negotiable. And yes, Oracle are and probably will still be the main contributor. There will be Long Time Supported versions though, but Oracle will not be supporting OpenJDK LTS, others will do that, like Red Hat. Oracle will support their version of OpenJDK, and give support to their paying customers. As others also will do.
Oracle JDK are and will be based on OpenJDK, there will be no differences as it was before OpenJDK 9. But if you want to have Oracle JDK, you have to pay for their support.
So no, it will not be a big issue, just use OpenJDK and/or others compilations, like those mentioned here in this thread, like Oracle, RedHat etc.
OpenJDK will have long time supported versions, which OpenJDK 11 will be one.
So the choice is the blue or red pill, as they said. Go on the rolling 6 month schedule, and have the latest. OR go for the LTS, which will be at least supported to then next LTS and probably longer.
OpenJDK are based on modules, and THIS is the big thing. The rest of the changes is just nice to have additions.
But modules ARE changes, so there have and will be removed methods, classes, packages and modules. Some notable is java.EE, which is Java Enterprise Edition, and web server support. You can get those from other support though, like today with many different Java Servlet Containers.
Modules are basically a collection of packages, where you tell which other modules you uses and need.
So, the main thing is Modules. And so OpenHAB should transfer to use modules, even if other libraries have not done the transfer yet. Yes, there are ways of temporarily ignore those module warnings, but they WILL stop to work, but for now we get warnings. So, warnings now will be fatal later.
There are gradual ways of transfers to use modules, but it need to be done.
Modules have the nice property that you can collect modules that your program uses, and create a Java RE that only have those needed modules. Which will make a smaller RT and a Java that uses less memory in distribution and when running. Yes, you can make a RT which IS your program. And that will probably be the preferably way of distributing programs.
That is with modules it will be like linking in GCC and other program languages.