It's easy to make something lean when you can start from scratch. Backwards compatibility and large user bases resistant to change are overlooked as primary causal factors of the modern state of affairs, imo.
Just want to point out that starting an OS from scratch, even if reusing an existing kernel, is a monstrous epic.
I find it difficult that one would be able to just use existing kernels like Linux without some considerable changes to support a more secure userspace (which seems like a requirement in order to do wild new things).
