Cisco UCS is basically simply compute gear (memory, I/O, storage).
UCS will not replace Ethernet switches as there is always going to be a need for a box to physically plug the compute gear into. Ethernet is not going away, even though they are trying to rename it to 'Fabric'. Fabric is marketing, Ethernet is IEEE standard.
VMWare NSX is simply an overlay networking technology. NSX traffic is tunneled across the underlying IP (layer3) network. So is OTV, and many other fancy new acronyms.
The issue with Data Center being the future is at some point the rest of y'all are going to realize, ...wait a minute, why do I want to worry about all this, and you will purchase utility compute from a trusted mega compute player - Google, AWS, OpenShift online, Azure.