if you tp yourself to 29999998 ~ 29999998, you'll notice that the terrain abruptly stops generating, and going into the non-generative terrain will kick you from the game even if your in single player, the message saying: "connection lost" "illegal position". after being kicked, your then taken to the multiplayer page.

one last note: if you jump straight into the non-generative spot, you are kicked and you cannot re-enter, as you will be kicked immediately before being able to move back to land.

If this is intended, then they need to revert back to the 1.7 invisible wall thing.

PS:

Pushing mobs into the spot will destroy them.