If this discussion has caught your interest and you have experience in Linux internals, you might be interested in joining the team at Boeing that is working towards broader use of Linux in aerospace. Here are two links to open positions:
Yes, that's it. We want to take advantage of the innovative technology in the "expansion" but need to carefully manage what we actually put on the airplane to demonstrate (with evidence) that it is well suited for the intended purpose. Which I think is what you mean by "consolidation".
Our point was a but more nuanced. We pointed out the problem (and also value) of the collaborative innovation. Then, we also noted that with some care, we think a carefully customized distribution could be shown to be sufficiently safe.
Linux competes not only on the desktop with Windows and Mac OS, but also on the server and cloud environments, and also in embedded environments. It is highly scalable to many use cases. No, we don't expect to use Linux right off the shelf. As the full presentation noted we would create a carefully curated profile to go on the airplane. And that work to curate and manage it, and producing certification evidence of correctness -- is definitely not free.
Using redundant systems helps detect (dual redunant) and even correct (triple modular redundant) physical faults in the system, where one system will provide a different answer than the other(s). System redundancy does not detect/correct for design flaws, which are a common mode failure. Catching design flaws is currently done by testing (compared to known correct answers) and peer review (by domain experts). Someday, mathematical proofs might be used (known as "formal methods"), but currently these are only possible to use on very small software projects, such as the seL4 project that formally proved correctness for around 10K lines of code.
In order to fly, current regulations in most countries require the aircraft is flight certified by the named regulatory authority. In the US for civilian aircraft, the regulatory agency is the Federal Aviation Administration (FAA). So compliance to their stated standards is not really optional. It is also true that compliance does not necessarily mean security or safety has been completely achieved. That is, even if one "checks all the boxes" does not guarantee 100% safety. So we also depend on professionals who go beyond simply doing the minimum but who truly care about the safety of the flying public.