We could have OSes that don't use files, that save state and are able to resume in seconds, and we can do all of that in C (I don't think we would want to but we could). Also there doesn't exist a world where grandma (or even the Kool kids today) is going to learn smalltalk in order to use an OS.
The main hurdle I see with all of this is hardware initialization -- how to handle, from cold boot, the fact that your network card has no idea what frames has been sent and what have it has been received.
The first step I see in all of this is creating an operating system where the kernel has no concept of being booted. One thing people struggle to wrap their head around with optane is "what does kernel upgrades look like" which would be messy in existing OSes.