SDN has been searching for a killer app since its birth in the midst of protocol and encapsulation debates of 2011. It wasn't monitoring, flow management or physical network orchestration for a controller. It turns out it is container networking.
Container is challenging the VM or a group of them is a unit of application. Its value proposition is removal of the virtualization tax and being open source it does not cost a whole lot to try out. The schedulers (k8, mesos etc.) seem to be maturing fast enough but the networking behind is still quite elementary.
Using offloads that accelerate encap/decap of an overlay network on the JEOS (Just enough OS), containers with virtual interfaces can outperform hypervisor based VMs and integrate better with orchestration technology like gubernetes.