Pain and hunger are the two main sensations that can cripple a person, preventing them from "competing" in the real world. I'm glad Watsi's tackling one of them. In my country, doctors are often equated to God, and Watsi should be commended for serving the same role.
That said, I'd love to see YC fund a company that can create more fundamental and lasting impact. Kalibrr, also from YC W13, somewhat falls into this category, even though it's positioned at a decently developed economic rung of society.
I'd love to see YC fund a company with a scalable model that can uplift a society and affect significant lasting change (doesn't matter if the company is non-profit or not). I guess this would require YC to fund more companies that're based out of developing countries and that have innovative business models. I'd like to think there's a lot of economic gain to be made in the process too.