In Adobe Lightroom there is a concept of "publishing service". Its a collection that has a "publish" option, which exports just the images added to the collection after the "publish" action was last triggered as well as those pictures that were previously, but they have been adjusted. It can export to disk/flickr/facebook etc. It also holds export settings, target directory, etc.
How to set up something similar in darktable? Currently I can export entire collection to disk and rsync the result to the target folder, but in case I add 10 pictures to the collection holding 300 pictures, then it means vast majority of pictures are needlessly re-exported.