As with every major release of Java there are challenges. But as Java 9 is overhauling parts of the core that can impact a lot of existing code out there, it needs more testing than some of the previous major releases.
So while the schedule is slipping from my perspective that is NOT a bad thing at all. Why? Well it gives developers a bit more time to try out Java 9 against their own software and make accommodations in their code if necessary. Otherwise you might be looking at scramble time. I for one would NOT want scramble time! So I would STRONGLY recommend you start testing against Java 9 builds that are available now. See https://jdk9.java.net/download/.
Posted September 14, 2016