I'm going to kick this post off by referencing a recently published article over at Seeking Alpha. It's entitled "4 Reasons for Microsoft's Xbox to Go as Big as Possible, ASAP".
The essence of the article is that the sizes of the 360's hard drive (particularly the Premium's 20GB drive) is no longer adequate for the current climate. Specifically, it speaks of a climate that Microsoft themselves are beginning to create, where the world of digital distribution will be the future. Indeed, one only needs to listen to the stirring words of Mr. Ross Erickson in the most recent Major Nelson podcast to understand how important concepts such as XBLA are to the fundamental belief system (the "DNA", as Ross refers to it) of the 360.
Recent rumors have suggested that the 20GB drive will soon be replaced with a 60GB hard drive as the standard size. While this would certainly improve the situation, I believe even 60GB hard drives are not going to be sufficient within the next 12 months. The mind boggles to think of all of the uses of the hard drive space that Microsoft has delivered or soon will: Video Store downloads (TV shows can potentially stay on the hard drive as they are purchases not rentals), game demos (easily 1GB+ each these days), occasional betas (also in the 1GB+ range), IPTV recordings (current successful DVRs ship with 120GB-160GB hard drives and fill up very quickly with the swelling sizes of HD content), game content (hundreds of Guitar Hero and Rock Band songs can add up!), and Xbox Originals (also 1GB+ each, some swelling to over 2GB), not to mention the ever increasing library of XBLA (and soon XNA) titles. So what is the solution?
At the very least, I'd like to see the 120GB drive become standard, and see a new 500GB drive become the new "enthusiast" drive. I think that 120GB will be a sustainable storage capacity during the 360's lifespan for most folks, and if the 360 becomes the primary cable box for IPTV users, I think it is reasonable for the larger drive to be an upgrade. The key here is that the 120GB would slide down to the $99 price point (and become the default drive for Premium versions of the 360), while the 500GB would be at the 120GB's current price of $180 (or less…:) ).
What do you think are reasonable thresholds for a new set of 360 hard drives? (And let's not start about user-upgradeable hard drives, shall we? That's why God Satan created the PS3…)