Just out of curiosity, do you know the marginal costs of hosting a free private repo? How much of your upkeep costs are hosting free repos vs paid?

There are no paid repo's, all repo's are free. The costs are very limited (low single digit thousands). We pay for it with money we get from on-premises subscribers. We think this will be like email, the storage costs can be offset with other income. Instead of advertising we're thinking about offering a marketplace (similar to what Heroku does). But that is a long term plan, for the next few years we're focussed on growing it.