To my mind this completely negates any value proposition of the container. The only thing missing, at face value, is something as straightforward as the Dockerfile for building base images. I imagine that shouldn't be hard using things like guestfish etc in guestfstools.
Lambda works great as a deployment and execution model. This allows anything to run on Lambda, not just specially prepared runtimes.
Prefer containers because build once run anywhere, as opposed to build for each deployment target.
When your container is not running (say, 99% of time), other customers' containers are running. No need to ever boot the kernel, etc.
One might say that an unikernel has advantages over it. But it also has a higher barrier to entry.