[mhays]

Those are incredibly short floor-to-floor heights. Add a couple feet for offices.

If the whole thing is physically buildable at some point, some basics will probably still apply:

A water park would pay a tiny fraction of the cost to build it (omitting the cost of using it to prop up the other 450 floors).

Fitness centers like to be on two or three floors, not 25. It's supposed to be easy to get from the weights to cardio, etc. Can't rely on the "stairs are exercise" point...even gym rats often don't want to stress their knees.

Shopping on 76-100...why put stores in a place that would be inconvenient to get to? I'll skip the long version. The brief one is "stores wouldn't lease there, for very good reason." As the "world's largest mall" you're presumably talking about floor plates in the 200,000 sf range on the lower 100 floors.

Why would you need 50 floors of dining?

It all sounds physically possible once construction materials and methods grow enough. But commuting to anything beyond the first couple uses would be hellacious. The number of elevator towers would be pretty epic to make it all work. To say nothing of the many stairs that would be required by anything similar to modern codes.

Regardless of what's physically possible, mixing uses and going tall would be extremely ineffcient use of materials and dollars. Even when the industry CAN do something like this, actually doing it would take multiple billions of dollars more than doing the same thing in a more typical manner.