SD-WAN is being pushed by many dedicated SD-WAN service providers as being a significantly cheaper model than traditional MPLS networks. The reasoning they give is that SD-WAN uses public Internet as underlying network technology. The business case becomes clear in their eyes as they propose to rip out all the existing network hardware, replace it with their new SD-WAN hardware and it is all paid back with cheaper public Internet.
So it is very understandable that when we talk to our customers, they see a direct link between SD-WAN and your normal run of the mill DSL or COAX public Internet line.
The larger carriers are keen to point out that you can run SD-WAN over MPLS and also they are correct both in their statement and trying to protect their installed base.
So where it comes down to is: SD-WAN is flexible in the underlying network technology. Modern SD-WAN kit uses deep-packet inspection to see what kind if applications are running and so the kit can map the application onto the required port, be it an MPLS port or a public Internet port. So you can have a hybrid solution and it does not need to be hybrid at each location.
The nice thing is that the application is even more the starting point of your network design than ever and that your network design needs to be changeable to cater for changing applications. All possible.