First: this is a controlled leak from Apple, of a fake design. Tim Cook himself said Apple is 'doubling down' on secrecy, which I'd imagine would already be in place. Part of such a strategy could include deliberately fake leaks showing half-baked case designs. This could be one of them.
Second: this is one of many prototype designs being tested in the field and not the final. Apple has working plan B's and perhaps even C's when developing a product, and this could be one of the lesser designs.
Third: This is a case that houses a more radical redesign. I'd imagine that the front glass panel may be real (I do see the logic in a 16:9 iPhone) but the case itself is a cover for a thinner and more radical design.
We have little idea what kind of technologies Apple will be cramming into the new phone that would affect design, so speculating on the final look is taking vague, uneducated guesses at best. But if it were up to me, I'd agressivley push for a radically thin case, possibly with tapered instead of square edges.
But that's just me. I could be way off since this is just speculation in a vacuum.