You are not paying to use Volumio, it is free to use. I am sorry that your questions were not answered on the forums; please remember that this is a Community effort to make Volumio a better experience for the Community.
This is a niche request, and you offer no reasons to make it so. Whilst it is possible in Raspbian, it is not clear to me what advantages it would offer that make the development time worth while.
Most people don’t use NFS. As to saving a copy of the database to a remote location, that sounds like a good idea, probably best achieved via a plugin.
There is a ‘backup’ plugin available currently, see Volumio Plugins Collection. This does not include music database, but probably could be extended to do so.