If I search the iTunes AppStore for SMB, there aren't a lot of apps that allow you to connect to network drives. Many apps support Dropbox and Google drive and other "real" cloud solutions, but not local NAS. It's a nice feature, but I imagine the demand is pretty small. I have a couple apps that do connect to NAS, GoodReader being one example.
I've found with my iPad and Network dive on my home network, I rarely use my full-size computer for any data transfer, but still get to keep several TB of data locally secure on the network drive, and accessible to all my mobile devices...but it's probably more complicated than most people want to maintain at home. But I keep all my Chinese PDF's sourced on my network drive, and it would be nice to connect more directly to Pleco.