The true edge of the 3D engine world is what a 3D engine like Irrlicht, OGRE, Unity3D, etc. can support, not so much as what the game can support or the kind of bugs in a game that would cause a crash at those coordinates. E.g. with Irrlicht's 32 bit single precision floats you'd need to go to somewhere in the order of 10^38. The problem is that from a 3D perspective things break down at that point, and even before that. A simplified example:

Knowing that we only have a certain number of positions to represent a number we can do a little demo as to what will happen. Suppose we only have 4 positions at our disposal to represent numbers, e.g. 1, 2017, 3.14, 13.4, 12E6, etc. Now suppose we are close to the origin, we can easily draw a 1x1x1 cube from (0, 0, 0) to (1, 1, 1) and build a world based on that. Or we could create quite detailed meshes/ objects to 0.01 accuracy e.g. a mini cube going from (2.04, 4.07, 1.11) to (2.05, 4.08, 1.12).

When we move away from the origin, things start to get a bit messy. At position x=1000, y=1000, z=1000 we can still make our 1x1x1 cubes, but those meshes with 0.01 precision won't work anymore (we cannot represent 1000.01, doesn't fit). The vectors defining a mesh's triangles get truncated and we start to see misalignment of the mesh surfaces. 3D engines usually start to show jitter and shaking of objects and the camera at this point, besides surfaces not connecting anymore (been there, done that in my 3D coding time).

Now things start to really fall apart when we get close to 10000 though, as that number no longer fits in our 4 positions based numbers. We introduce the exponent in order to support these larger numbers and represent the coordinates with a simplified exponent notation like 10E3, 12E4 (10 x 10E3 = 10000, 12 x 10E4 = 120000). The funny thing now is that we make jumps of 1000(!) when using 10E3 and 10000(!!!) when using 10E4. Things get worse and worse and worse the further we go away from the origin. However our poor man's floating point system still allows us to travel all the way to 10E9! Not that our game can do anything sensible at those coordinates, all 3D breaks down there basically ... Plus anything in the game that can't handle these kinds of situations causing it to crash ...

The above is a very simplistic view of course, floating point works a bit differently than what I described. There are other problems that limit a game like Minetest/ The Game That Should Not Be Mentioned Here even more severely than float limitations e.g. the noise generations stops functioning properly at some point, see

http://minecraft.gamepedia.com/Far_LandsAnyways, the game just stops generating the map at some point to avoid problems, but from a 3D engine perspective it is perfectly valid to keep on going beyond that point!