Well, while we are getting rid of the old OS, so all the applications need to be recompiled anyway, lets switch to the Mill Computing Platform. Why? Number one feature for an OS, there is no such thing as a ring zero. All applications, including the kernel, run at the same pace.
Now, couple that with all the benefits of the Mill Architecture.
* Next, lets start with seL4 as the Kernel, as the only mathematically proven, verified bug free kernel*.
* Add Vulkan as the only Graphic API,
* Switch to ZFS for large clusters of Hard disks,
* Switch to an SSD optimized Filesystem for appropriate hardware,
* Add different flavors for the OS. seL4 has this idea that the OS interface is simply made up in how applications pass information. So, you can setup a Windows passing scheme, a Genode passing scheme, a gaming specific passing scheme, an OS X passing scheme and so on and so forth.
You can then have applications written directly to the metal, or locked to one particular scheme.
Yes, I know that it doesn't work quite like this, but we are dreaming, aren't we?
* Yes, this assumes no bugs in the verification and all that jazz.