You might have heard the news already: JDK 9 is going to be delayed by half a year, now aiming for a March 2017 release instead of its original September 2016 target.
Since Spring 5 is designed to track JDK 9 very closely, we decided to revisit our own roadmap as well: We are nevertheless going to start our release candidate phase in Q4 2016 but we won’t go GA before March 2017 either. That said, we really mean it: The goal is for Spring Framework 5.0 to go GA right after JDK 9’s GA date then.
The opportunity for you to start working with Spring 5 features will begin much sooner anyway, with the first Spring Framework 5.0 milestone scheduled for June 2016…
In the meantime, our spring-reactive R&D project is making a lot of progress already; feel free to chime in with design feedback at this point! The reactive R&D project will get merged into Spring Framework 5.0 proper when the actual 5.0 branch starts next year.