Maybe the bold solution would be to port the Serenity userland + UI stack across to Linux and be very staunch about what gets into it. Essentially grafting the Linux kernel in place of the Serenity one, and using its UI Kit and WindowServer instead of GTK/QT/X/Wayland.
Maybe it might even be possible to preserve the logic and non-UI libraries of many applications, even if the UI required a complete rewrite.
A bit fantastical but just putting it out there.
It is fast and open source. But very tightly integrated into google and so I doubt, this will ever become a solid base for a new linux desktop.
They use a custom kernel. A completely different display manager, process scheduling, startup etc.
But yeah, rsync works the same.
It'll be, once the realtime patchset is completely merged.
Meanwhile, some distributions (including Arch) offer a pre-patched kernel.