My ideal solution actually is in Apple hands.
What I want them to do is to build in remote, home NAS accesability into app apps, actually deep into the OS itself. So in reality I don't need to store any Music, Movies, Books, Podcasts, Videos on the device itself. Just Apps and some small local storage.
Everything else is stored on my Home NAS device.
At home I get it super fast over WiFi and when out and about I get it via Wifi over the internet.
That's my Ideal senario.