They could also charge for git-annex I think. It is not that they need their own type of private repo's to charge for that. By the way, GitLab.com offers unlimited repo's and 5GB per repo for free.
How many users/how long will you be able to provide that for free?
Forever, our business model is to make money with on-premises software (GitLab EE). In the long term we might add a marketplace to GitLab.com were you can subscribe to additional services (like Heroku does).