So, here's what I want:
1) New map - Hyrule was great, but if this is "only" a heavily tweaked Hyrule I will be mildly disappointed. I love exploration, and seeing a changed world is quite a few steps back from seeing a new world. In that vein, I'm hoping that the sight of Hyrule castle is just the opening and the end result of it is the specter of Ganon bolting out to the east across the sea or north across the canyon or something.
2) More polish - I honestly am hoping that BotW is the prototype for the next generation of Zelda games, just fine tune everything. Gimme more weapons, more combat variety, additional cooking depth, some smithing mechanics to repair/upgrade weapons, additional Sheikah Slate abilities like the hookshot, magical abilities, and greater enemy variety.
3) Actual dungeons - being able to come across dungeons in the open world, in caves or underground or in the middle of the map, whatever. Merge some of the open air greatness of BotW with the dungeon game from earlier titles, and that's a beauty.
4) Water depth - a notable deficit area for BotW for me was the water aspect of Hyrule, as there was really nothing to do there but slowly swim and to act as an early game barrier. Give me iron boots or a Sheikah Slate scuba ability to explore river beds and the bottom of lakes and ocean floors and find some dungeons there too.
BotW is my favorite game of all time, so I have extraordinarily high hopes here.