I'm wondering since there are wild horses if that means your horse can die and you will have to tame a wild one. Would be a cool feature.
That would make me feel terrible if I lose one at all.
Yeah, it's the whole reason I got that demon horse in skyrim, I didn't want my horse to ever die. The only mod I ever installed was also to make horses move faster and have more health. I was heartbroken when I finally bought a horse and then I accidentally ran off the side of a cliff and killed it. Nothankyou.jpg ESPECIALLY not Epona.
Also, I've been thinking about stuff that they could do to fill in the overworld. Obviously, the best thing to do would be mini-dungeons, like the caves in twilight princess, with treasure at the end. It would be neat if they could have these procedurally generated with a random treasure at the end. That said, who knows if they actually do anything like that. You could actually do stuff similar to wind waker, as well, where the caves were identical on the inside, but had different tasks (usually kill waves of enemies). If you recycle assets, you can sprinkle these everywhere.
Related to treasure, i'd love the treasure/upgrade system from skyward sword to return. You could make insects collectable again and have them spawn randomly throughout the world, where appropriate. Twilight princess only had TWO per region and once you caught them, it was pointless to catch more. If you make them a resource (tradable for rupees, used to upgrade, used in quests), then filling the world with insects (or some other collectable wildlife) gives you a reason to run around the open world. Same thing with SS-style treasures, used for upgrades, quests, etc. Have ore come from veins randomly placed along the world (like an MMO), have golden apples be a random rare drop from trees, etc. It gives you a reason to randomly jump off your horse and approach something you spot while riding.
The last thing is the enemy encounter from the E3 trailer. I'd love more BIG BAD enemies that are really tough to defeat and just spawn at random (but not too often) and chase you down. It'd be nice if it kinda forced you to run for a little bit before you could fight them. Make them really threatening and possibly invincible until you reach a certain point or gain the higher ground or have enough distance between you, or something. You could also have enemies like the soufflee from KI:U that run away from you, but if you catch them, you're rewarded with rare treasure.
Sure, none of the stuff I said is really SUBSTANTIAL, but it's still something nice to do in the open world and has precedence in other Zelda games.
Also, since the world is so big and there is a day/night cycle, there should probably be a way to change day/night, like in OoT/WW. Rather than a song, it'd be nice if you could build a fire/make a tent and sleep out in the open.