I've been thinking what could be a good addition to the open world formula but also help with some shortcoming the Zelda games have.
One thing that comes to mind is helpful microtransactions where you can buy rupees and bottles for real money. In every Zelda game I've ever played, slashing grass and breaking pots to get no more than 1 or 5 rupees is one of the most unsatisfying feelings in gaming. Seriously, picking up 1 rupee is so unsatisfying, especially when you're going for a 500, 200 or even a 100 rupee item. So, something like:
$9.99 - 100 rupees
$19.99 - 200 rupees
$29.99 - 500 rupees
Collecting empty bottles is also often unsatisfactory. Give me an option to buy 4 empty bottles from the start so I don't have to bother with that for the rest of the game.
The other one is invasions. Links can invade other links. The flow of time is distorted in Hyrule and you can easily find yourself in another player's world. It would also spice up the timeline discussions quite a bit. You can really get crazy with this. Other players will want to kill your Link and get his resources (proposal: maybe you lose half your money). However, you can also prepare your Hyrule, so to speak. Hyrule could be made into the ultimate sandbox playground and you can mold it to your liking to some extent. For example, you can chop trees and collect materials to craft bear traps, pits, etc.
Or they can also implement a perk system. Let's say you choose a stealth perk for Link where he can go invisible for 30 seconds. So you sneak behind the invading Link and spray him with a horse attracting spray. Now, when you turn visible again, you run through some horses, and when he chases after you, they get attracted to him and start chasing him, and potentially the stampede kills him.
So I guess my suggestion is make Hyrule the ultimate sandbox and really streamline the boring stuff that's a staple of the Zelda series, like rupee collecting and empty bottles.