> I like his ideas about tighter vertical integration between the OS and desktop apps, and a browser that is a smart document reader, as opposed to a VM for web apps.
Other actively developed OSes that fit this level of OS + desktop apps integration are:
ReactOS: https://reactos.org/
Haiku: https://www.haiku-os.org/
Redox: https://www.redox-os.org/
> Bonus points for non-POSIX plays or language choices beyond C/C++/Rust :)
Then you will pretty much like Fuchsia, a new OS by Google that is actively developed in the open and uses its own kernel called Zircon which is a microkernel optimised for modern processor architectures and multi-core machines.
Several drivers are actively written in Rust and its networking stack is written in Golang. Everything else including the kernel is written mostly in C++11.