Graduate the feather across a selection - Photoshop

A tool that works similar to the gradient fill.

With an active selection instead of feathering it by just a set amount of pixels you have the ability to feather it from e.g 0.5px to 15px and you draw across the selected area in a particular direction as if filling with a gradient. Option to select linear, radial etc

Not a tool designed for complex masking, but as a tool for quickly creating mockups, cutting elements out with shallow depth of field etc... 

Mockup to help explain better below