Treat the include processor like any other extension, and allow it to be replaced
For generating pdfs for aggregated pages, from an .adoc file that includes the desired normal .adoc files (such as could be generated by changing the xrefs in a nav.adoc to includes), I need a slightly enhanced inclusion processor. It's easy to make the existing inclusion processor self-registering, and allow it's replacement by something attached to the asciidoc config.