Dynamically loadable modules

Short: Allow you to specify a non-existent module at compile time like you could with action. 

Why:

You want to try a module from 1.6, but 1.5.x is the latest release
You want to develop a module, and you want to keep track of your changes on git
You developed a module, and you're waiting for a pull request to be accepted but you need your co-workers to use it
You developed a module and never intend to share it with the world

For all of the above cases, you no longer need to maintain your own ansible fork.