I agree with the first part but simplify the "why they'd do it":

• it's easier to choose with nice marketing
• corruption.
• being able to externalize IT.

As for the rest, from what I've seen:

• Web infrastructure relies on open source. Military critical OSs are a custom from open source. Security is best working from open source.
• You can pay the same maintenance fee for open source programmers for chasing your targets, leading to Ubuntu, opensuse, LibreOffice teams.
• upgrade is debatable. In the end i'd guess you're more often better off with your hardware or national servers, but that's related to security.

Consumers will like it, then enshitificaction. Also your data anywhere in the world.