The problem is that NSX and it's derivatives is entirely based on virtualized environments. But, at least in the SMB world, much of the infrastructure still runs on real iron. Therefore NSX represents only a partial solution. We told VMWare this several months ago and got a mostly ho-hum response: "We don't do that and it's not on the road map."
At best, NSX is a partial solution to the requirements for network security at all levels of the network. However, the only other players are networking companies which, while they do a decent job at the network switch and router level, their virtualized security solutions are cumbersome. too complicated to use, and produce a serious latency in communication becase of the requirement to hairpin all communication through a real network device.
We're looking for a good universal solution. The company that can produce a unified security solution that runs in both the network hardware AND the hypervisor stands to be a real winner. However, it doesn't look like anyone even recognizes the need.