But they had a year to make that change. If Trev's source is to be believed, we're getting at least one of the NX devices this year.Given the speculation based on the patents, that would seem to be the case. Also, extra controllers improve processing power of the console. And placement of haptic buttons wherever you want.
On topic, if it's a real leak (IF), it doesn't necessarily mean it's the final form factor.
Here's an actual early prototype of the Wii U Gamepad:
Nintendo also changed the 3DS style slide sticks to actual analog sticks before release. So anything can happen between now and reveal/release.