We knew almost a year ago that you'd be stuck with the Xbox One's 500gb hard drive. Much like Bewitched's original Darrin, it is irreplaceable.
Our concerns were met with assurances that you could simply use external USB storage, but the One's launch came and went without such capability. Meanwhile, One owners are sitting on 391gb of usable (for games) hard drive out of the box as the console library slowly grows. Real slowly.
Microsoft's Larry "Major Nelson" (of Bewitched competitor I Dream of Jeannie fame) Hryb took to the Xbox One subreddit to say that, "External game storage is coming soon....I need to check on media support." As exciting as it is vague. No details yet on a possible cap for the external storage size (the 360 capped at 32gb, which would be sort of useless on the One).
Xbox One [Reddit]