The video of the rootless containers talk from Devconf.cz 2019 is finally available on YouTube. The talk covers how user namespaces, fuse-overlayfs, and slirp4netns come together to allow running containers entirely as an unprivileged user, without any setuid helpers beyond newuidmap and newgidmap, and discusses the remaining challenges around cgroup resource management and overlay storage performance that still need to be addressed for rootless containers to reach full feature parity.

https://www.youtube.com/watch?v=jMOHfCw0DV8

If you are interested in the slides, they are available here:

https://www.slideshare.net/AkihiroSuda/rootless-containers