Nice initiative, this Wikipedia Zero!
The Foundation published an article about Net Neutrality. Their argument (stating they don't break the principle) is quite solid, and you used it in the past: Wikipedia is not a commercial service, it's common good. We can make a parallel about calling the police or the fire brigade being free of charge on telephone networks.
So what's your point? You fear Facebook et al. will invoke zero-rated Wikipedia as an argument to ask for the same, thus breaking net neutrality?
Thanks for sharing anyway, this is great news! See you!