I'm several sets of information short of being able to say anything particularly precise about their results.
Their diagnosis is very detailed and useful, but I think the main thing we can learn from it is that the Linux kernels VM system is horrible when memory is overcommitted. At least to me that's not news.
I will also say that we in the Varnish project have not worked much on performance the last couple of years, because people have asked much more for features than performance.
Some of the stuff we have done have traded CPU cycles for flexibility, but if the Varnish users change their mind and decide performance needs a boost, we can do that too.
The reason we dropped sendfile(2) in Varnish was that nobody seemed to be able to show any credible performance improvement, and dropping it allowed us to implement on-the-fly processing of the HTTP bodies in a cleaner way.
We can certainly bring sendfile(2) back for "the straight" path if that's important to people.
The "file" storage was our first rather primitive storage engine and it has never been optimized to any extent. Varnish Software Inc. has a commercial offering that includes a "massive storage engine", but most people seem to just use the 'malloc' storage.
And no, Varnish is not dying just because BBC doesn't use it in the absolute far corner of high-end usage doesn't use it: If NGINX is the better tool for them, they should absolutely be running NGNIX.