Academics can sometimes learn a lot from industry. The ScyllaDB database and its underlying SeaStar library essentially implement a userspace OS that handles the hardware very differently than a typical modern OS with phenomenal improvements in performance.

Historically, it started as a unikernel called OSv designed to run directly on hypervisors. But they eventually realized that it can run just as well on linux with kernel bypass working and io_uring and is easier to deploy.