I'm very, very excited about this. The poor level of control over permissions in orgs were a big issue when we (LXQt) moved our development to Github. Look forward to trying it out.
Edit: Here are in-depth docs on the new features: https://help.github.com/articles/improved-organization-permi...
The new collaborator feature makes it easier to include stakeholders in the communication loop.
The feature I really think github is lacking right now is the ability to give selective permission to some sections of the repo (issue|wiki|code|releases). Right now the only way to share issues but not the code is to create a separate repository, which is cumbersome to do and maintain for every project.