What's the advantage of enroot over charliecloud, which is unprivileged in the sense of being installable in your home directory (given user namespaces)? https://hpc.github.io/charliecloud/
It is the same idea, we actually considered it at first.
There are some differences in the implementation though and we built enroot with the idea of being more extensible.
We also have a plugin for SLURM (https://github.com/NVIDIA/pyxis)