Theory: Remix 10's Location

Abstract
Remix 10 from Super Mario Run is the same land as the Special Worlds in Super Mario 3D Land and the Lost Levels from Super Mario Bros. 2 (JP)/Super Mario Bros.: the Lost Levels.

Arguments

 * Argument 1: They seem to be an unconnected world from the rest of Mario's Planet and isn't connected to the map since it's always changing locations and areas.


 * Argument 2: The only way to seemingly get to Remix 10 is through a pipe.


 * Argument 3: the background of Remix 10 looks a lot like the background of the Special Worlds, having bright neon colors and transparent-ish hills.


 * Argument 4: Remix 10 is stated to be "A World".


 * Argument 5: The levels in Remix 10 are remixes of the levels from the base game, much like many of the levels in the Special Worlds.