"The problem is that I have no idea how to tell employers that those (SO, GH, etc) are the places to look if they want an accurate description of what I can do

"The problem is that I have no idea how to tell employers that those (SO, GH, etc) are the places to look if they want an accurate description of what I can do." So you are looking for a concise and centralized resource for listing your qualifications for a job. And you are asking if a resume is still relevant? It seems like the way to tell employers about your github, SO, udacity, etc, profiles is to list them on your resume.