I’m already using syncthing + nextcloud together in my setup it’s actually something that I prefer to use, so that I can have an independent node that I can use to access the data, without being a syncthing node.
The reason for that is using nextcloud as a UI (app is decent, web is fine and universal) to access to the data I’m syncing between my machines with synchting.
So basically, I’ve a syncthing snap installed in my main node server that is synchronized. Then the nextcloud snap which mounts the syncthing folders root (I had to use bindFS to make sure the permissions / owners match), this way I can upload things via WEB UI or app and get them in all my nodes, or at the same time access to them when I’m away.
I also had to use a inotify based script (inotify-exec.py + syncthing-nextcloud-inotify-bridge.sh) to monitor changes done via syncthing in order to update nextcloud of the changes promptly, however this might be done better by just monitoring syncthing via web API, but I just went for the faster development path 
This is something that could be in some sort be optimized and made possible even at official level.