You'll note that I said “simplest” – this could work on a $2/month shared hosting plan (not sure where you got the “updating and restarting httpd” bit from with a couple decades of prior art showing otherwise).
The Jetty approach is clever, too, as would be things like scanning rel=prefetch links but simple declarative approaches have their moments, too. One thing the Jetty approach doesn't appear to offer is the ability to manage resources if not all resources are appropriate for every client so it would appear to do things like ship every size of a responsive image to every client.
