Earlier quoted context omitted.
I would imagine it would be really hard to make the voxel coordinate system spatially coherent over the whole planet, so placing smallish regions of buildable space at various geotagged points seems like a pragmatic approach. You could still design it to get the types of interactions you're after. Edit: To clarify I think it’s hard because of the earth not being flat but also because of the difficulty of syncing AR t…
Good point about the coordinate system; you'd run into one sort of trouble or another if you want to go with anything that's approximately "cubes" (i.e. say each voxel is a "cube" of fixed height × fixed #degrees of latitude × fixed #degrees of longitude) unless you exclude two circles of the planet's surface from the game (say, some radius around each of the poles), and even then, you would have to contend with voxe…
I assume the center of gravity of such a world would be the actual center of mass of however the voxels are arranged, meaning players could affect it with large enough structures or small enough worlds. Without adjusting "straight" "horizontal" structures to conform the curvature of the world, gravity would no longer be a force that was normal to the surface of the structure at some points on it.
I can also imagine people digging to the center of a world to find the gravity flip-flop point and playing with it. Or hollowing out the interior of the world in order to get a zero-G chamber (assuming no atmosphere) [1]. Or building gravity trains [2].
[0] https://imgur.com/a/0J5RoE1
[1] http://hyperphysics.phy-astr.gsu.edu/hbase/Mechanics/sphshel...