If SDN is an architecture, then what is the technology? Clearly it is not virtualization, in fact, most SDN architecture are not yet virtualized. It is not a protocol. The whole point of giving software the control is not to be constrained by a protocol. It is the API. API is what makes SDN possible. APIs like a network stack is not monolithic. There is the free API i.e .REST and there is the premium API which may or may not be proprietary - but will always be Open. APIs come with their own infrastructure and scaling that infrastructure is the challenge of SDN.
Moving on to business model of SDN. It is not in selling controllers. There are too many of them. It is not in scripting, integrating and scaling them in a cloud infrastructure like say OpenStack. Those are what is normally called out as NRE in the ROI spreadsheet. The business model of SDN is in hosting the cloud. SDN lowers the barrier to entry to enter the business of hosting.
So if you want to make money off SDN, get into hosting. If you want to work on SDN, get into APIs.