You really need to back up these assertions with some evidence.
Do you have benchmarks that show the impact of switching to userspace on a typical, loaded desktop system with all kinds of workloads? Or are you just guessing?
I did not anticipate a Hacker News discussion about a remotely exploitable Linux kernel WiFi vulnerability requiring some network benchmarks on an unusual network stack architecture, but I'll oblige:
This publication (http://www.minix3.org/docs/jorrit-herder/asci06.pdf) claims that MINIX3 could saturate a 1 Gb/s Ethernet link with an user-space network stack, with separate processes for the stack and the driver, on a rusty 32-bit micro-kernel that can't do SMP. In 2006.
Do you have benchmarks that show the impact of switching to userspace on a typical, loaded desktop system with all kinds of workloads? Or are you just guessing?