I’d like a few things to be improved,
Firstly, better dungeons. Whether this will take over completely from the shrines (personally I’d prefer it, could keep the health/stamina upgrade system in place whereby you get the games version of spirit orbs from doing side quests) or not is another question but I felt BoTW massively missed the dungeons of previous games. Not really fussed how many dungeons they’d include but as long as they were better than the divine beasts I’d probably be happier.
Secondly, scrap the weapon durability and have previous items return. You could then have an upgrade path like in Skyward Sword where you can upgrade the items to increase their power in battle to compensate for not finding higher powered weapons in the wild. I didn’t mind the durability system overall but it seemed to swing massively from early game items having shocking durability to mid-late game weapons having enough durability but by that point you’re getting so many high powered weapons thrown in your direction I just found myself switching them out all the time anyway so I rarely actually broke many weapons in the latter parts of the game.
Thirdly, better and more in depth side quests. As I said in point one, you could get spirit orbs (or whatever they call them in the new game, if they keep them in the game) for completing side quests so you can upgrade Link’s health/stamina to your preference. Ideally there’d be a lot more to them than collecting items, some of the side quests in BoTW were good though, I liked Kass’s shrine quests and there was a few others I enjoyed but I felt they could have been a lot better for the most part though.
Lastly, more music. While I enjoyed the soundtrack there really wasn’t many memorable tracks in there, probably none that I’ll still be humming years after hearing them for the first time like with Gerudo Valley, Dragon Roost Island, Stone Tower (heck a lot of the music from Majora’s Mask is amazing) and so on. Edit, just dawned on me I have done a massive disservice to one of the best tracks in the game that I might actually still be humming in years to come, Kass’ Theme
Some things I don’t want to see changed too much (but a slight improvement would be welcome) is the combat, physics engine (having more traditional items at Link’s disposal would give people a lot more ways to mess with it as well) and the graphics, personally I loved the look of the game.