Actually, now that I've reviewed it, there's a conflict between this patch and the current behaviour. At the moment, the way to set the output directory to something other than target/generated-sources is to set the output configuration parameter. If this is a directory, generated files go into that directory. If that option is set in the defaults section of the schemagen config, it affects all of the generated files. Tl;dr: there is already a mechanism for changing the default output directory for all generated files.
Voting to reject this patch until it's clearer why users need two mechanisms for achieving the same end. Ian