Its an cycle of 6 months in the new model. You have to adapt your libraries very 6 months to the new language standard.
So... you can't just use the standard of the current stable release that runs for 3 years? Then I got that a bit wrong.
I don't really see this being enforcable. You compile a library with the JDK LTS version it was developed for and there should be no problem... it's not like Oracle is going to send you seize and desist letters because your open source project isn't up to date.
I'm so glad I spent my time learning the C++ powerhouse.
I'm very glad I learned C++ too, if mostly for the understanding of how code works it gave me. Professionally I've never used it. While Java as a language is only marginally more convenient than C++, the JVM is a hell of a platform for anything that doesn't need the best possible performance, and the Java ecosystem is a juggernaut .NET has so far unsuccsessfuly attempted to displace. And Kotlin is on a good way to replace Java as the goto language for starting new projects on the JVM, and it's the most beautifully designed language I have ever seen.
Basically the only reasons not to develop your server architecture on the JVM are .NET legacy code, contractual obligations or some *serious* need for speed.