This seems like a good question, and I also hope someone with good knowledge/experience around this to give some good comparison. I have given only very cursor

This seems like a good question, and I also hope someone with good knowledge/experience around this to give some good comparison. I have given only very cursory look into QNX and Fuchsia/Zircon and it seems that one of the main difference is the capabilities-based architecture in Fuchsia. It's a big change in the API/conceptual model, but we'll have to see if that actually translates into a meaningful difference at the application level - e.g. whether it allows building new types of applications, or allows building meaningfully more secure/fast/reliable applications.