To imagine the question lets have the following scenario:

> 
> We have Terraria (a 2D Platformer revolving around harvesting
>  resources and building stuff). We have a large 3D sphere populated
>  with resources (static) and creatures (dynamic and reactive). If the
>  world of Terraria was 3D instead of linear 2D (with 3 layers in the
>  3rd dimension in total), what are the different ways one could deliver
>  the visualization of such a world/game?
> 
> 
> 

The example I have given above is for a 2D Platformer based on a 3D world. For the above case - the question is easily solved somewhat by converting the 2D platformer into a top-down planar game (Civ V to a limited extent - again represents a cylinder not a sphere; Rimworld nails the top-down solution almost perfectly, but some rasterization using tiles was required) - but lets avoid that and explore some better options.

Another example I would like to give for a top-down 2D planar game based in a 3D space:

> 
> We have a classic Top-Down space invader shooter, in this case, space
>  is completely flat and planar - with limited depth in the 3rd
>  dimension. What if the depth was infinite in the 3rd Dimension? What
>  if the dimensionality of battles in realistic 3D space games were more accurately
>  simulated instead (attacks arriving from multiple dimensions - and not
>  just the same plane)? Ofcourse, keeping the 2d concept of the
>  visualization itself in mind. What are the different ways to make this
>  possible?
> 
> 
> 

And also, *is it even practical?*

This is not easily solved by turning the UI into a platformer. Homeworld tackles this only to a certain extent - but it still limits the depth and reduces the significance of the 3rd Dimension.