Can a Jmod explain the entire DLC package situation?
DLC wasn't really the right word. What the team were referring to were the Membership Access Packages, which will be how Steam only users can access Membership. We'll be detailing those closer to launch, but that's what they were referring to.
If it helps, the reason the word DLC was used is because those Membership Access Packages will appear under the 'DLC' section on Steam - just the way that platform's terminology goes.