- Improve the design a bit. Carefully, you do not want to piss of old subscribers.
- Improve the conversion rate. There is a middle ground between newsletter modals and burying the method to subscribe.
- Introduce a few new products. As far as I can see, at the moment it is just "in depth news for OSS, especially kernel hackers". Maybe they could package some parts of this up for different audiences (security notices, content partnerships etc.).
- Some marketing tactics. "Invite a new subscriber to get this badge." SEO could be improved, too.