Add a premium tier, even something as simple as integrated web analytics. Donations are charity. If you want this to be a sustainable business, ask for people to pay for value.
And if they add a premium tier... well then that kind of kills their differentiation, doesn't it? They're aiming for the niche of free, modest, simple, laissez faire vis-a-vis content. When you take 'free' out of the mix then you're in the arena of commoditized cheap hosting; inertia would be the only reason for someone to upgrade their free account to a premium plan.