Combined with the idea from the article to offer two distinct networks (one traditional, private, WPA2 and one open, only allowing VPN connections out) this sounds like a very practical idea. Is there any good reason not to do it this way other than to protect financial interest of mobile carriers?

A very paranoid regime could even establish rules to only allow certain accredited VPN providers (e.g. ISPs) to free people who offer open WiFi from the fear of being prosecuted.