> 1) implement privilege isolation for subsystems and 2) implement subsystems in a more secure manner, both of which absolutely improve security posture.

Sure, but Android already has that via a user per application for app sandboxing & a very extensive selinux policy set[1]. Which makes the real-world benefit of that seemingly very negligible. There's a huge gap between desktop Linux & Fuschia/Zircon here, but there doesn't seem to be a particularly big gap between Fuschia/Zircon & Android Linux.

1: See all the .te files in the public & prive dirs of https://cs.android.com/android/platform/superproject/+/maste...