Late-Game Crafting Grid Upgrade

As you know, a player's crafting grid is a 2x2 space. This limits a player's crafting capabilities without a crafting table. Once you use a crafting table, the grid is upgraded to a 3x3 space. I would like to see a difficult, late-game way to upgrade to a 4x4 grid, allowing players to craft more complex and powerful items and blocks. I know that there's been a lot of talk about End Biomes. Maybe there could be a tool found in End structures that you could use on a crafting table to open the 4x4 grid. Of course, your standard item recipes would be available on the 4x4 grid, but the recipes for the late game items would have to be uncovered in order to use, so Enchantment Books could be placed into slots beside the 4x4 grid to unlock crafting recipes. I am unsure of what exactly players should be able to craft with the upgraded grid. I am open to suggestions!