> something faster

How true is this, really? When does the OS kernel take up more than a percent or so of a machine's resources nowadays? I think the problem is that there is so little juice there to squeeze that it's not worth the huge effort.

The problem isn’t direct overhead. The problem is shit APIs like blocking I/O that we constantly have to work around via heroic extensions like io_uring, an inefficient threading model that forces every app to roll its own scheduler (async etc.), lack of OS level support for advanced memory management which would be faster than doing it in user space, etc.

Look behind the curtains, and the space for improvement over the UNIX model are enormous. Our only saving grace is that computers have gotten ridiculously fast.