In fact the firmaware v2 allows to enable / disable NFS using the UI although it is not documented anywhere. I found it out recenty, by chance.
Log into the dashboard, and go to ‘Shares’ section, and under ‘Set up shares’ you’ll see the list of your configured shares (at least the Public one).
Click on any of them and you’ll see the ‘Share Access’ area. There you can enable FTP and NFS access to that specific share. You can even configure the mountpoint address and the range of allowed IP’s. This overwrites the fstab file and (I checked) is persistent after reboot.
You have to enable the option share by share, it’s a fast process unless you’ve created many shares.