I think you misunderstand what the openconnect initiative does. It both reduces costs for ISPs and speeds delivery of content to end users. The ISPs no longer have to pay for the extra upstream bandwidth and network equipment to handle that load. The amount saved through that vastly dwarfs whatever small colocation fees would be gained if they charged. If Netflix is accounting for a significant portion of the traffic on the internet, then it's accounting for a significant amount of traffic that ISPs must handle, and that's a large amount of their overhead.

That said, I wouldn't be surprised if Netflix will/does pay some amount to colocate in some instances. The economics in some instances may cause the amount paid to be less than the cost of the CDN traffic.