Neil Cybart, writing for Above Avalon:

The Apple Watch Sport band takes up nearly four times as much wrist area as a Watch case.

By this, he means that the Apple Watch body consumes just the top part of your wrist real estate, while the band goes all the way around, with lots of “wasted” wrist real estate.

Obviously, this ratio will change depending on the user, but the primary point is that simply utilizing the top of our wrist is not optimal for wrist wearables. While the top part of the wrist is ideal for viewing data, the rest of our wrist can still be used for other purposes.

Including additional sensors, battery volume, and other components directly into Watch bands will better utilize wrist real estate. Instead of having the Watch case be the only “smart” piece, Apple will likely begin selling Watch bands that go much further than just representing pieces of fashion.

And:

We likely got a glimpse of this future when looking at the New Yorker’s profile of Jony Ive which mentioned that he admitted much of Apple’s Watch R&D was focused on the bands and not the rectangular Watch case.

Interesting post, lots of solid conjecture. Two obvious watch band solutions that strike me:

• Batteries that can charge your Apple Watch and, in a pinch, your iPhone, too.
• Better sensors for more accurately measuring pulse rate.