It may or may not be apparent, but NSX for vSphere is in many ways the next version of vCNS. In my lab, I’ve attempted to keep vCNS while adding NSX to the same vCenter server. The license key or configuration apparently overlap; if vShield Manager boots up first, NSX indicates that it’s not licensed. If NSX manager boots first, the vShield Manager states that it’s not licensed.
I did not, but should have, performed an upgrade from vCNS to NSX and now will have to add NSX Edge Gateways to replace the vShield Edges.