Kubernetes support for docker user namespace remapping
So, it's not supported yet like Docker as per this (as alluded in the comments) and this.
However, if you are looking at isolating your workloads there are other alternatives (it's not the same, but the options are pretty good):
You can use Pod Security Policies and specifically you can use RunAsUser, together with AllowPrivilegeEscalation=false. Pod Security Policies can be tied to RBAC so you can restrict how users run their pods.
In other words, you can force your users to run pods only as 'youruser' and disable the privileged flag in the pod securityContext. You can also disable sudo and in your container images.
Furthermore, you can drop Linux Capabilities, specifically CAP_SETUID. And even more advanced use a seccomp profile, use SElinux or an Apparmor profile.
Other alternatives to run untrusted workloads (in alpha as of this writing):