It could be selling digital copies on iBooks, Amazon, with B&N. It could be packaging curated collections as a paid periodical. It could be anything, and all without compensation to the authors.

Some ideas:

- optional domain names

- custom branding for companies wanting a blog engine

- sponsored articles linked from home page

- as others have mentioned they could create e-books based on popular topics

if they're ever going to do ads, you know it'll be in a fancy 48px font screaming at you...