Seems like the starting point for this would be e-readers with open device content control. So instead of relying on my_email@kindle.com or something like that in order to get files onto the device, you’d use your own file server or something for the device to connect to.
Then the long-term ownership just consists of having the epub, mobi, or pdf files of the books you want to own, and passing them through whatever device content control system you’re using.