Definitely just fixing retail. My wishlist...
Aesthetics:
- Unreal 4 graphical update as well as much larger zones/cities.
- Super deep character customization. Individual choices for every feature, small/medium/large, colors, age/weight/height sliders, the works.
- A dye system like from the Witcher 3 for gear. Nothing outlandish, but maybe 10-15 new colors for all gear.
- Reintroduction of glyphs, only much more expanded upon. Customizable spell colors and visuals, etc.
- Mount Armor like in ArchAge
Gameplay:
- Reintroduction of many RPG elements such as: Racial traits, Resistance, Tier sets, Hybrid tax, Hunter deadzone, Reagents, positional attacks requirements, Attunements, Keys, Guild Perks, etc.
- TBC/WoTLK-era Talent Trees. 1 Point per level, meaningful choices, and varied spec styles
- Re-implementation of TBC/WoTLK era professions (specializations, alternate gearing paths, pve/pvp boons)
- Reversal of mythic+ dungeon rules such as not being able to use profession items and toys in dungeons and raids
- Reversal of camera zoom distance limitations
- Reintroduction of 10 man raiding and removal of raid difficulties (LFR doesn't count). Every raid has easy, medium, and hard bosses with optional hardmodes.
- Player Housing: At least Skyrim level where everything you collect in the world can be displayed/stored visually in your own home. Set displays, trophy room, taxidermy, home decor, paint, landscaping, etc. All obtained and unlocked through various gameplay
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Player-created Content my own idea back in 2015. Basically a world-editor, so people can create their own instanced content. Warcraft 3 Custom Games proves how wildly successful this could be.
There's a lot more to expound upon. This is a good start, though.