In the last couple days ideas and code for doing asynchronous writes to clients has started to flow. Brian Pane has posted a cool diagram of how the different connection states might work. On Saturday I created a subversion branch at https://svn.apache.org/repos/asf/httpd/httpd/branches/async-dev/ to house the development. If anyone is interested in helping shape Async IO development, please go and criticize our plans on dev@httpd.
I hope to have time to post a more detailed description of the work and ideas on this blog.... Maybe later this week.