Probably never.
With more people streaming video and audio than ever before, and assuming that trend will continue on.. the need for ultra-large capacity hard drives will probably only exist at the enterprise level in the future.
I often get the impression I'm one of the very few people in the world that actually record HDTV content and rip blurays.. and this is where you start to require multiple TB's.. an uncompressed Planet Earth series BR rip would weigh in well over 100GB for example.
I'll be thrilled when we finally get a 3 or 4 TB drive with a solid track record.. :whiste: