The following information comes from a Game Informer interview with Eiji Aonuma...
On stepping away from the usual Legend of Zelda development process
In the recent years, Zelda games have become like a development order and workflow that we followed. We wanted to create something that wasn't that. We wanted to go off the rails a bit.
On stepping out of the Zelda comfort zone
We had to redefine how we develop games. In the past we took an approach where we would create small areas and patch them together, but then we realized that we couldn't do that with this huge world. When we created this huge world, we first had to figure out what we needed to place on the map. So we figured that out, and then we would play the game every day and revisit it, and figure out if those elements we placed would actually work in those areas.
We would have (the staff) play the game over and over repeatedly and really have them take the time to understand what they were creating, as well as understanding the whole entire world as we were creating this game together.
We created a rather huge area where people can explore, but we soon realized that when you restirct these areas and create a boundary, then people always want to go outside of it and wonder, "What is out there? What is on the other side of the boundary?" I realized that I had to take out the boundaries and create this area where players will be able to freely roam around.
Fun in dying
I wanted to create a game where users could have fun dying. If you wanted to, you can go fight the final boss from the get-go, you don't have enough power or stats, so you can't defeat the boss. But through trial and error, we want the user to figure out when they may be ready to battle the final boss and know when that time is, which they can decide on their own.
If there is a little spike of difficulty, you can always go around it and avoid it until you are stronger or you are ready to fight it. You can always revisit that difficult area you may have encountered.
Link the loner
Link is kind of a lone wolf in this game. I wanted to create that feeling so that whenever he encounters somebody, he has the element of, "Oh, I just saw somebody!" and the warmth that you would feel.
Companion characters in the past have always navigated and showed the path, and because we wanted players to choose their own path, we didn't want the companion element there to distract the players.
Aonuma on playing other games and their influences
In the past, I didn't play many video games. Then I realized this isn't right. I have to. So nowadays, I actually play a lot of overseas titles. I played Skyrim. Grand Theft Auto? I'm not really into violence that much, so I don't play it. I also played Witcher and Far Cry. While playing those games, I do find some ideas, but it's not that it connects directly to Zelda to where I would take something and use it in Zelda. It's more of something I keep in the back of my head while developing the game.
On letting players figure things out on their own
I heard that American users are more eager to figure things out on their own, rather than having to go and find certain items in certain places. I am actually the same way. I wanted to add that element to Breath of the Wild.
On telling the staff about the Switch port
Asking the staff to change it was difficult for me. I actually went back and created a proposal for my staff that said, "Hey, if you do this, then maybe you can fix this area," and I had to make that proposal to the staff and beg them to do it. Those changes are gameplay related, so they are reflected on both platforms.
Aonuma on finding surprises right at the end of development
Right before we completed the game, I actually started from scratch with a new game. I was trying to explore areas I remembered from my memory, but I kept finding these new elements, and I realized how huge a world I had actually created. That was right before we had finished the game, so you could tell I was surprised.