Google Summer of Code/2017/Ideas/USE flags management
Write a tool to manage global and local USE flags as well as expand variables, review them, audit them, filter them based on various criteria, etc... Get inspiration from:
Integrate it into emaint. The code will have to be written in Python and use the Portage API.
As it is unlikely this is enough for 3 months of full-time work, you'll have to be creative enough to expand the features sets of USEful and/or emaint in a meaningful way.