In the thread mentioned by the OP, Gregory Kurtzer (CEO, Sylabs Inc.) just added:
Apologies that the thread got dropped, but our interest certainly has not changed. We have begun two projects which will help on this initiative:
An OCI compatible interface (both CLI and library) to Singularity. This is a good path forward for community compliance, but it won't support features like cryptographically signed containers via SIF or encryption as they are not OCI compliant.
Because OCI doesn't support all of our features, we are also developing a Kubernetes CRI gRPC shim which will allow us to interface Singularity into Kubernetes at the same level as Docker and Podman. This will allow us to support all of our features under K8s.
Also, please note, that we have also prototyped and even demo'ed Singularity running under HashiCorp Nomad for services and AI workflows.
The OCI, Kubernetes and the Nomad work in progress will be opened up in the coming weeks so stay tuned!
In the meantime, a tool like dgruber/drmaa2os
does have support for Singularity Container.