I would like to see us able to craft and repair our weapons, shields, and bows.
We already gather resources and mine away at deposits to get some minerals and such. Why not add in some ores to the mix?
I could see each town having a blacksmith with every stable having a traveling blacksmith. Then we can spend rupees and the necessary ores to repair our favorite weapons (especially Amiibo gear) and possibly even apply upgrades such as the perk modifiers or even upgrade the weapons base stats.
It would also be a great way to make use of the "lower level" weapon/bow/shield 3D models.
After all, in BotW as you level up via the hidden-exp system, you stop seeing many of the weapons. For example in my current playthrough, most of my weapons are the Royal Guard versions of weapons, with the exception of my Amiibo weapons and Kilton's goofy hammer.
With the inclusion of a Blacksmith, you could have them smith you some weapons/bows/shields that are leveled to your stats.
Want to have a Knight's Broadsword because you want to cosplay in the Hylian Knight armor?
Well now it isn't a detriment to your offensive capabilities by having a Blacksmith craft a Knight's Broadsword with 65 damage!
ANOTHER great thing to add to Tears of the Kingdom would be the cut elemental class from Breath of the Wild.
You know that one Yiga greatsword weapon that let out a gust of wind, the Windcleaver ?
Well, fun fact, that is one of the only weapons of its class that is from the mostly-cut weapons class known as "Gale".
Fire, Ice, Thunder, and Gale.
Gale includes the Windcleaver, Deku Leaf, and the Boomerang type weapons. But it was supposed to be so much more.
Gale Arrows are a prime example, being a ranged weapon that did impact damage but also knocked surrounding enemies off their feet if they were small enough.
A "Gale Rod" would've been interesting to see implemented if that was even supposed to be a thing, with a "Hurricane Rod" being an upgraded version similar to how the Fire Rod has the Meteor Rod.
Perhaps a Windcutter being a one-handed version of the Windcleaver?
A Typhoon Shield allowing you to knock-back a group of enemies with a single parry attack?
Perhaps the Toon Link Amiibo could gift you the "Gust Jar" from The Minish Cap, Twilight Princess Link's Amiibo gifting you the "Gale Boomerang", and Skyward Sword Link's Amiibo gifting players the "Gust Bellows"?
All of which being able to push a raft with their wind powers while having combat capabilities so you don't have to just carry a leaf in your inventory.