Matt,
We have two options to fit your needs and I'm curious how close they match your vision.
First, we have
Asciidoclet, which allows you to write Javadocs in Asciidoc format and renders the output into the standard Javadoc html. This includes a number of benefits including the minimal code-readable syntax and support for Asciidoc plugins. See
this for examples.
Second, a related project we've been putting together is
exportdoclet, which allows you to export javadoc comments into asciidoc tagged files The intention is to allow you to reference your javadoc comments within via asciidoc include statements.
Let me know what you think.