This Steam package does need exclusive content so I'm planning to cover at least two exclusive topics:
Game Design Practical Tips - What I've learnt for building a fun experience and keeping it manageable for a solo developer. (I'll aim for a May release)
The Road To Greenlight - At the end of the GTGD S3 tutorials I'll take the project forward and turn it into a fun game, and show how I approach Greenlight. (End of project release)
When GTGD S3 is complete I think the price will be somewhere from $9.99 to $11.99 so anyone buying it now is getting the learning package at a good price.