Two years ago, there was a discussion on asynchronous request processing in OpenRasta: http://groups.google.com/group/openrasta/browse_thread/thread/34a599e21bf65d53
Googleing 'openrasta' and 'async' doesn't yield much more than the above link, and a quick grep through the source code (http://svn.caffeine-it.com/openrasta/trunk/src) did not look promising either.
So is it already possible to prioritize requests (so that IO-bound ones get queued, whereas quick ones will always be processed synchronously), using asp.net?