Board Thread:Suggestions forum/@comment-34969473-20180601001728/@comment-27190591-20180601101500

This is more complicated than you think. Theraerel is right, simply increasing the world height would cause major performance problems (depending on the amount of course). What you need are cubic chunks, so that not the whole area 16x16xchunkHeight will be loaded but only the relevant sections. This is because a chunk curently covers the whole world height (bounds: 16x16x256). There is a mod trying to achieve cubic chunks (but for 1.12): https://github.com/OpenCubicChunks/CubicChunks/wiki/About-the-mod. If you read the wiki and look at the code, you'll see that this is anything but trivial - the amount of work needed for this is immense. So I don't think that this will ever happen.