But it’s not like you just plug in a hard drive full of content and never touch it again. You will want to be adding new stuff and probably pruning back old stuff.
I would way rather serve video to my ATV from my iMac or a NAS, where I can add/delete/edit files -- versus having a drive connected to the ATV that I have to physically move and connect in order to add stuff.
But that’s you. I imagine you like having a NAS and spent time playing around with it. I know that’s exactly what I do with my NAS.
I’m talking about simply being able to use the AppleTV as a TM destination (which is something Apple haven’t offered since discontinuing Airport) and a place to store you photo library once it gets big (and they do get big, my photo library is 220 gigs, and that’s just 25 years of personal photos, bit professional work).
For a household with an AppleTV and a couple of MacBooks, say anew and a MBA - a NAS is over complicating something that could be done within existing hardware in the Apple ecosystem, and is also an extra expense. When you factor in the drives, even a budget Nas is a chunk of change for something that people don’t really think about, because when it’s working properly you shouldn’t notice it.
Using iCloud storage as the alternative can because a very expensive subscription over time, adding up the months, once the amount of data grows larger.
There’s a gap in the Apple eco-system for this, an iota-small ultra simple NAS, basically a TimeCapsule without the focus on also being a router, and the Apple TV, being positioned as a “home hub” already, and having all the necessary hardware already, bar the external drive, is the perfect fit to fill that gap.
It’s simply the iCloud subscription fees that stop Apple from allowing this to be done, imho.