It's no secret as to why China would set a firm deadline. Officials know VPNs are regularly used to get around the Great Firewall and access blocked services that might host political dissent, but merely making these private, secure connections illegal won't deter people. It has to make the very act of accessing a VPN difficult if the law is going to have any teeth.
This is bad news for free speech in China, of course, as it makes eluding censorship that much harder. Moreover, it may hurt businesses that are just trying to get work done. What if you're visiting China and need to use a VPN account to access business info while you're away? Not every company needs or can justify internal VPNs in China, and it's not always an option to visit someone else's offices just to check a website or send a message.
Thankfully, this isn't the only way of dodging the censors. Open proxies like Shadowsocks are still around. The question is whether or not China will clamp down on these alternatives as swiftly and thoroughly as it is with VPNs. Historically, solutions like Shadowsocks tend to be reborn or adapt in the face of threats -- there's just no guarantee that they can keep it up forever.