This article is arguing that SDN on the WAN is still not there yet and it is naming some products and solutions that might be able to fill the gap. But SDN on the WAN is only half of the solution.
To what, by the way, but that is a different discussion. I can argue that current protocols like GMPLS (thanks @mbushong) and PCEP are already filling that gap in the WAN. Depending on the definition they are very close to SDN.
But this is still only half of the solution. What you want in the end is inter-AS-SDN. Especially for delivering global VPN’s and services from OTT-providers. If you need some kind of openness in the provider WAN, with this you need even more openness and the current BGP trust-model would have to be extended. I don’t see this happening very soon.