Music disc item,
Book item - Supports raw JSON,
Embedded Raw MCJSON Generator - For tellraw,
More wide ItemStack use(NBT) - For some "better enchantment table",
Multi-Effect Food/Drinks - That's quicker than doing a procedure,
Quick Procedures(Like I suggested) - That's quicker than exiting from item editor and losing everything,
Redstone-like Communications - For some generators, etc.(As I know, you already are going to add FE)
Now for methods:
-Distance to highest block below given entity - I will use it for my boss.
-True eyes height(y+1.6) - Can be useful for ^ ^ ^ coordinates(if 1.13), otherwise I don't know tbh.