Botw needs weapons buying/selling, weapon crafting and arrow crafting badly.
Yeah apart from crafting Ancient weapons, that's one area that kinda sucks...With a bit of exploring you do get weapons constantly, and if you know how to handle the overworld bosses it's a decent way to get more weapons as well without sacrificing too many of the weapons you have (Lynels and Molduga tend to give some pretty decent weapons)...but at the same time I would like to be able to keep some weapons...
The Champion's weapons are the only ones that can be repaired (though I'm keeping them in my house in Hateno)
Adding a smithy to the game that sells weapons as well as allows the player to craft and even repair weapons can really help at times...
To make it harder, only certain smithys can work on certain weapons...however the higher weapon classes can work on weaker weapons as well...
for example all the stables could have smithys that can craft and repair the Traveler's weapons, respective races could have smithys for their weapons, and on rare occasions you could find a 'master' weapon smith that can craft and repair Royal and Legendary weapons...
It's just one area that I can see be added in future games for sure...
as for Arrows, it's actually fairly easy to farm arrows from enemies, I spent about 20 minutes in one spot and ended up with over 300 until the enemy ran off for some reason...