Its very likely that most of the challenging security stuff will continue to move down into the kernel itself. Its important to remember that the entire concept of a container wasn't really a single unified concept in the Kernel until very recently as they've gained popularity; instead, they were a amalgamation of a few different capabilities in the kernel.
Perhaps, you caught news of something I haven't seen, but AFAIK, "container" is still defined in user space. Talking to Eric Biederman, that's what the kennel team wants - people to experiment in user space, remixing kernel tech together...