I'm playing along similar lines as the OP. Using Linux as a base avoid a whole lot of code that is basically uninteresting to me (eg, drivers). And using Pyth

I'm playing along similar lines as the OP. Using Linux as a base avoid a whole lot of code that is basically uninteresting to me (eg, drivers). And using Python (in my case) makes prototyping ideas quick and easy. I've defined a "pseudo-kernel" API, which is implemented either using the Linux kernel and/or C libraries or uses various (small) services to emulate other functionality that would be in the kernel, if (or when) I end up writing it. I can deploy to a Pinephone, a Raspberry Pi, or a PC trivially, and I can mostly test things on my laptop under macOS, which makes for a fairly productive development cycle. Which means my few hours a week generally progresses things meaningfully, rather than being bogged down in the mechanics.