...a "report" query that let you grab the tree at some point and have the server hand you everything below it.
That would be harder with the KHG because each page is assembled on-request by CGI scripts. We might want to add the indexed kernel source to the KHG at some point, so it might be nice to be able to choose whether or not to include that in the response to the request. :-)
So I don't think it is a trivial operation.
If the sources to the server used here are available, I'd take a look and see how hard it would be to add...HyperNews feel very free to take a look at it and implement similar functionality for it. I'm sure that it would be useful for far more than just the KHG; HyperNews is used to run a lot of other sites as well.