I’ve also been thinking for this option. But usually it’s good to use also separate backup technologies for different destinations for reliability reasons. If you only use Duplicati all of your backups could be totally ruined.
Yet in situations where I need to have files on multiple locations, I’ll usually run backup to local storage drive, and then mirror the data set to destinations using whatever tool works best with that destination. rsync, robocopy, ssh, webdav, sync (with whatever destination having it’s own sync app). - This works very well.
But it’s always important to have that alternate backup, unless duplicati won’t work. Also having local backup set (duplicati or not) is very important for restore speed. The remote backups are only for total loss of site, cases. If something needs to be restored, using (more or less) local source, like NAS is much better and faster option.