I absolutely love the idea of exploring the fracture between the two timelines - as you said, so many fantastic opportunities to explore there, both narratively and in terms of gameplay. Also, I wholeheartedly agree with expanding the world; when it was released, A Link To The Past (definitely one of my top 3 favorites of all time) felt absolutely MASSIVE in terms of the world to explore. I think that there is plenty of lore to draw upon to create a vast, achingly beautiful Hyrulean landscape that builds upon that living, breathing world foundation that ALTTP first laid down.