Even the current 30 million block limit is artificial; you can check the actual code yourself (search for 30000000; this is for 1.6.4, before they added a wall, explaining how "fake chunks" happen; the code simply returns 0 instead of a block ID, etc, after that point); there is no viable explanation for such a limit in terms of what variables can handle; a 32 bit integer can range from +/- 2.147 billion, so they added that limit probably just to have a hard limit on world size - not that anybody would ever have a problem with it.
Also, I suspect they removed the original Far Lands by going from single-precision to double-precision variables; the accuracy of single-precision is close to the 12.5 million block limit; double-precision has far more accuracy, enabling a vastly larger world size (millions of times) before the math goofs up or integers overflow*. Of note, some things still goof up because they use single-precision variables, such as the position of torch flames (in 1.6 anyway), but when I tested it I didn't get any of the jittering present in the Far Lands or Bust videos (your position uses double-precision now).
The hard limit where chunks are overwritten is at X/Z of ±34,359,738,368, which is about 23% of the distance from the Earth to the Sun. At X/Z of ±2,147,483,648 (crashes at 2,147,483,439), item positions, mob pathfinding and other things using 32-bit integers will overflow and act strangely, usually resulting in Minecraft crashing.