The problem with interactivity lies in with whom the user is interacting. If the content is served from a CDN, where does the interaction go? Back to the content owner? It doesn't know the context of the interaction. To the CDN? The more interactivity is required for Web-site control or video delivery, the more the serving of the content from a CDN starts to look like just moving the whole host process to every metro area. That, of course, is likely to run up costs. Of course, if you're a telco or cable company that wants to serve IP-based video on demand to customers anyway, it makes sense to use the same tools to provide interactivity to CDN-hosted videos. In fact, that could be a valuable differentiator.
Another issue is that of "operationalization." The Internet traditionally has been a best-efforts network, and so CDN performance traditionally also is best-efforts. In fact, for a given video experience, it would be difficult to tell just what piece of the delivery infrastructure created a perceived problem with quality. For telcos, video probably will be a premium service with performance guarantees. If you're a telco who stays awake at night worrying about how to support millions of premium video customers, who might call with complaints, you don't want to build that service from pieces that don't have telco-compatible management interfaces and alert-handling. Standards bodies are working on the management of complex experiences made up of content, network resources and even hosted applications; but CDN players aren't part of the groups involved. The telcos are; and by pulling CDN functions into their own infrastructure, they can get quicker solutions to operations problems.
None of this is going to cause the death of CDNs. The original mission of CDNs, in fact, is probably as essential as ever -- or more so. The challenge is that these changes could create pressure on prices for CDN services as the telcos enter the market, and the interactivity and operations requirements could force CDN players to deploy new equipment that would raise their costs.
On the positive side, the changes the telcos want could create opportunities for new services and for differentiating the CDN incumbents. If CDNs advance far enough, it probably would discourage at least some of the telcos from getting into the space at all. But there's little chance that big changes aren't in store for CDNs, and anyone who thinks otherwise is probably in D -- for denial.