I've seen several workalike kernels in various stages of completion. at least one of them was able to run some pretty substantial applications (Postgres, nginx, that kind of thing), and that is still I guess around 250kloc. but it only really has drivers to support hypervisor devices.

unfortunately as time goes by, the linux api surface gets larger and more convoluted. so there's going to be some coverage you're just never going to get.

but in the abstract, definitely. linux is so bloated at this point that its not clear that it can ever be 'made safe'.