The grsecurity post is technically correct .. but that's how Linux development is always done. First lay the foundation, then fold over subsystems one at a time in piecemeal increments.
Everytime grsecurity comes up someone asks why it is not in the main kernel yet. The short answer is that the developers couldn't or didn't want to work that way. Kes Cook is actually nibbling away at that work right now, doing the thankless work of merging one part of grsecurity functionality, one piece at a time. That the first commit isn't complete or even very useful is to be expected.
Although GKH's pithy response on G+ hits at their incentives: "it's hard watching your business model slip away, I feel bad :(" https://plus.google.com/+gregkroahhartman/posts/2rM46nj9RsL
Separately, KernelNewbies is my go-to place for high(ish) level summaries of kernel work across the entire kernel (not just headline features). http://kernelnewbies.org/Linux_4.6