Just based on your examples, I don't think that these types of questions would be a good fit here. Programmers, and Stack Exchange in general, work best when you're trying to solve a specific problem and don't know what to do. The Q&A portions of the site don't really support teaching or broad questions well, and broad, discussion-based, and/or opinion-based questions tend to be discouraged.
However, there is a chat mechanism that could be useful. The Programmers chat room, The Whiteboard, tends to be active. The level of activity varies, but there are quite a few regulars. You can talk about these broader subjects there. Other sites may have active chat rooms as well, for various topics.
How does one develop an operating system and other system software?
This would likely be closed as too broad. There are entire books and courses on these subjects. If you were reading a book and had a specific question that wasn't made clear in the book or after researching other sources first, that may be on-topic, assuming it was focused enough.
What is the make up of programs which run things like appliances, remote controls, and so on?
Again, this would likely be closed as too broad. There's just a wide variety of examples. We do have a history of similar questions being acceptable, but I suspect it would have to be something specific and noteworthy. There's a difference between asking about the software that runs in a random make and model of a commercial product and things like the Curiosity rover or space shuttle. It also depends on if we can reasonable be expected to be familiar with the internals of the software or have access to publications that discuss it to quote and reference.
How could I get my hands on this type of code?
This would be closed as off-topic. This would be one of the "resource request" questions that we currently have a custom close reason for. Searching is the best solution. Since you're looking for open source code, searching something like GitHub would be more efficient than asking a whole bunch of people to effectively do the same thing. The answers that would be generated also wouldn't meet our quality guidelines - they would essentially be links to repositories and maybe brief descriptions of the project, and how hows and whys for solving your problem.