kilbop - Any transition in platforms presents opportunities for new technologies at both the control plane and the data plane. Many existing boxes do not support VXLAN (from any vendor) and features such as those will vary at the data plane level. Configuration objects northbound, southbound programming, and how addressing and forwarding are resolved are included in the ACI architecture. Contrast that to software only overlays which require you to have multiple strategies per hypervisor, physical, WAN, compute, storage, and now moving in to the campus. The architecture for ACI covers these areas, including investment protection for existing platforms.