One of the key questions in the definition of this space is how much functionality to put into a central device like this and how much to distribute to external devices. Adding content caching might seem like an obvious candidate for a central server like this, but that would mean that it would have to be able to directly handle DRM negotiations with a number of content services and then negotiate with display devices in the local network. A better approach might be to have a central server that provides storage service to a Roku or a smart TV and lets that device handle the negotiations and encrypt the data on that central server.
The same applies for IoT devices on the local network. If the gateway exerts too much control over them it is likely that it will be bypassed. There should be a defined set of services in the gateway that enhances the devices without being too obnoxious about it. Example: A home router provides connectivity and a firewall that limits aspects of that connectivity. It also provides standardized mechanisms for computers and devices on the network to modify the settings on that firewall so that they can provide services.