Commands or (better yet) a block like the command block for machines to use when powered or a certain fluid or item is inputted. This could be useful in a weather machine (/weather rain), a global beacon (/effect @A haste 99999), and probably manyother machines.

This thing already exists, it just isn't documented at all. You place a command object in your json and in it a command string and optional int value interval (or something like that) in ticks, if -1 or undefined it fires the command when the crafting ends. Also supports chat messages. Found this today in the source code and commit history.