Minecrafts coordinates are stored as 'real' numbers (as defined by the IEEE 754-2008) - not intergers so your claim "This MinecraftForge mod extends Minecraft height and depth. The only limitation is size of 32-bit integer." is wrong the actural limitation is the maximium float value of -Inifinty to +Infinity (or 1.175494351 E - 38 to 3.402823466 E + 38)

You are right but also wrong.

Minecraft entity coordinates are floating point numbers. Specifically, double precision floating point numbers.
Rendering is done with single-precision floating point numbers (with clever tricks to keep the numbers involved reasonably small at huge coordinates in most cases).

Block and Tile Entity positions are 32-bit integers. Chunk positions are also 32-bit integers. Since 32-bit integers have smaller value range than double precision floating point numbers, they are the limitation.