The Linux kernel is a gigantic attack surface with a ton of legacy stuff most modern applications will never need. Namespaces do not really help with this, but userspace kernels can. (Haven't looked into Ginux enough to know if it does.)

That is also why I believe the namespace approach, and by extension Docker-like containerization, is a dead end when it comes to isolation. I hope something like gVisor will win.

This is even more important since agents have turned isolation from a datacenter topic into everyone's concern.