See i have done the same stuck a 1tb on the 360 console itself an its chewed up alot very quickly, I have a 2tb network drive plus a few other drives to add too, I work in IT lol, I just feel despite the xbox 1 been a new gen console, that the drive you would attach to it would be just a 2tb, Then for games going as blu ray now, could, i mean COULD be up to 50gb, nt to say it will be when at the moment games could be up to 8gb yet we have games at less than a gig. if a game is 50gb it will be something huge.
I plan on getting something setup in place for if and when i do bother to get the xbox 1, As no I have the jtag and also acess to the devkit options why run when you can walk