If I run 'site' as one of the goals of a multi-module project build then the
generated sites are copied as execution proceeds so the last module executed has
its site copied over all the previous ones.

By default, a multi-module site is generated in target/site and links are
generated pointing to ./[sub-module-name]/ - perhaps the copying could do
something to preserve this? Then the generated site would work from the browser
without requiring deployment.