Cool! I suspect that you can do some reshuffling to avoid using any locks when serving cache hits. Also, if you want to serve large files or live video, it may be cool to be able to have the coalesced requests send body bytes to the client before the upstream request is finished. I implemented this feature at one (non-varnish-based) CDN, and other (varnish-based) CDNs seem to support it for some subset of configurations.