Currently when developing Web UI addons you have to either copy over sources into a WebUI checkout or you need to have your own build process and copy over the produced artifacts to the nuxeo war folder.
In order to provide an experience similar to the development of core Web UI addons developpers should be able to at least simply symlink their Web UI addon source folder into the Web UI addons folder and have Webpack dev server handle the build as well as the the merge of labels.