That's the interesting thing about a post like this; it starts to form an argument about a principle like "no dynamic native code generation in the kernel", which clearly isn't an accepted principle today.
I'm not sure what I think about that principle, because native code generation is exotic today, but probably won't be 10 years from now.
But either way: your statement is exactly the point the post is trying to make. It's not "Linux is insecure", or "SMEP is worthless". It's "how does native code generation interact with the roadmap of security features OS developers and hardware manufacturers are planning"? Also, of course, it's "JIT spraying is cool and fun to implement, and here's a new place to try it."