The export to files and the upload to [insert your service here] is tedious. Also I at least tend to upload photos multiple times by accident.
Ideal scenario for me would be to have an album, or even better smart album, synchronized to Google Photos/Amazon Photos/maybe still Flickr/etc. automatically and directly. Maybe even hierarchically preserving sub-folder structures. One can dream.
That only Flickr would be supported seems a bit … outdated, esp. given the recent changes with Flickr.