nvpy has been designed for the largest part around the simperium / simplenote sync protocol and servers.
However, you *can* try the text note mode to work directly on a set of text notes on your NAS. This will only work when the NAS is actually available.
I _was_ working on an extension to nvpy that would support having something else sync the database (e.g. dropbox, owncloud, synching,) and then would be more careful about listening to changes happening on the filesystem, but I didn't get much further than the very start.