He mentions that fb noticed significant performance improvement [1].
You should see improvements in some cases, ie. when you can do zero-copy transfers (avoiding kernel->user and then user->kernel data copying), in other words when you pipe data from one socket/file to the other socket/file.
> I ran a simple HTTPS web server with net/http, loaded a page on Chrome, and instead of causing a kernel panic...
Followed by demonstrating it working.
However, the point remains that he only got it working up to doing a toy hello world. The part that would be important for performance would be what he mentioned isn't finished, which is allowing it to be used with sendfile so that web servers can just sendfile over a TLS connection and let the kernel handle all of the IO.