Plus there's a connection to Ocarina of Time
The Link to the Past sequel, which has no real official name in North America still, will indeed feature a light and dark world like the original game on Super Nintendo. That's according to CNET who interviewed Zelda series director and producer Eiji Aonuma.
Eiji also shared the inspiration behind how Link can now flatten himself so he can move along walls and it inspired from Ocarina of Time! It's based on the Phantom Ganon encounter and how he would jump into six identical paintings on a wall. "What if Link could have the same power," Aonuma stated.
I expect this slow trickle of revelations will continue well into E3. Oh Nintendo, you know how to tease.