Quote fromQuote fromThe performance issue is why I think the air block should stop after a point. The game would no longer have to render/place/ect that block, cutting down on the performance that is needed to slightly increase it.
The air blocks are used to reserve space for new blocks, so you can't just get rid of them. Without them the block arrays would get very tricky. Air blocks don't need to be rendered, so there is minimal performance loss compared to other blocks (but this amount is magnified because there are a lot of them.)
From what I've read about yMod, it sets a chunk's height to the highest non-air block inside it. It can do this while you're playing, so each chunk is only as high as it needs to be. I'm definitely going to try this mod once it gets updated.