Hashicorp's Nomad basically is just that, supports various way of running stuff too which is neat. Shame about the license change which basically killed all my interest in it, so seems the hole is indeed still unfilled.
You can still add pods if needed and the systemd integration works.
Plus you can actually improve isolation by co-hosting services under separate UIDs.
Like any container it is just co-hosting, and elasticity is a bit slower with autoscaling instances, but it removes most of the complexity of K8s which very few org benefit from or have the culture to support.
Though as I recall, it makes heavy use of consul, which I have used in anger, and makes me a little weary (though that experience is likely very out of date).
Some self-reloading HAProxy in nomad to automatically assign URLs to services when needed. Could have used Consul but meh.
Tailscale for private networking.