You should take a look at GPUs. All of the complexity of 3D rendering is implemented in userspace, and that has been the case universally in production for mor

You should take a look at GPUs. All of the complexity of 3D rendering is implemented in userspace, and that has been the case universally in production for more than 5 years now -- closer to 10, really. If you replace "all" by "almost all", you can go back much further than that, really all the way to the beginning of GPUs' existence. And yet normal application developers don't have to care, because the driver does it for them. The point is, drivers don't have to live in kernel space, they can live in user space as well. Networking folks may start being more serious about this nowadays, but it has been the reality in GPUs for a long time.