...and my god it has been awesome. Certainly more awesome than any instability it may cause.
> It's the equivalent of a desktop OS where any installed application runs in kernel
Most major operating systems give extension capabilities to enhance them in deep ways. My Windows install has ClassicShell as a start menu replacement and DisplayFusion for multi-monitor taskbars. I have explorer plugins for Zip files, Git, and Subversion. Any one of those tools can crash and take down the whole desktop process.
What you're describing isn't a modern power user OS -- you're describing iOS. A safe secure place where nothing interesting happens; only exactly what Apple has already imagined you could want.
> Not only a bad written extensions can have disastrous consequences
My browser crashes? Hardly disasterous! And then I can just uninstall any unstable extensions.