Custom PlayerController feature?

Currently there's a way to add and remove features from the player controller such as; Camera, Input and so on.

However I don't see anything in the documentation showing how to add our own features and I don't know how to access the code for the current ones.

I basically want to make a custom top-down camera feature and replace the current camera feature. Where do I start?

Start from making own player controller, is easier than you think or just copy source of default player controller and modify it that way 

I'm making an isometric game too and I did it like this: I turned off the camera feature in the controller and made my own camera control component. I also changed how the player walks, on start I turned off the feature movement and wrote mine in the player component and I assigned my own input via Vector3 PlayerController.WishVelocity

So the default player controller is very moddable. You can write own MoveModes. And if you don't like something, just pull it from repo and change it to own namespace. 

Where can I find the source code for the PlayerController?

You good Sir are a gentleman, and a Scholar. Thank you.

disable the camera feature and make your own in a separate component