For people looking to test and play with this on Linux and Mac OS X:
You can set the configuration option in nextcloud.cfg: showExperimentalOptions=true.
Then you will be able to also see the setting for virtual files and you can enable it.
However, because we don’t have file manager integration yet, it works a bit simpler. All files are replaced by an empty file with the .nextcloud extension. There are no correct icons or thumbnails and the file sizes are shown as 0 bytes. But when you click the file, it gets downloaded and opened and with a right-click you can configure things.
Help with testing this is of course very welcome. For Mac OS there are API’s in the system for us to connect to, this is simply a matter of some work. For Linux, we are talking to the biggest desktop teams (GNOME and KDE) about a way to make their file managers aware of the virtual files and show appropriate metadata.
As always, input and contributions super welcome!