Mark Reinhold of Oracle has confirmed the release schedule change following no objections from the four month pushback. The general availability date for Java JDK 9 is now set for 27 July 2017 while the feature extension completion deadline is 22 December. The firmed up schedule was posted today to the jdk9-dev mailing list. This is actually a secondary delay after JDK 9 was originally talked about for shipping in September of 2016.
Java 9 is set to bring HTTP 2.0 support, garbage collection improvements, the new jshell command line tool, improvements to the Process API, Unicode 7.0/8.0 support, AArch64 (ARM 64-bit) Linux support, GTK3 support on Linux while retaining GTK2 support for Java applications, and the reason for the four month delay: Project Jigsaw. Jigsaw is the effort around a standard module system for Java SE.
More details on what's coming for JDK 9 can be found via the Java.net project site. New features are specifically talked about here.