Awesome that the folks at Roomie are so responsive. Now I'm feeling bad as I had used the DDK to create a custom Chromecast device and had been using this functionality for months without sharing. :/
Maybe Roomie should be snooping in on what custom devices users are enabling in the app in order to discover all kinds of new features they could be adding. Wait. Nope. No! Nevermind.. I didn't suggest that. All kinds of privacy implications. Someone is bound to be posting passwords to a URL or something.
It's a shame that Google doesn't add a HDMI-CEC command interface to the Chromecast API as this would instantly make it one of the cheapest, most readily available CEC control devices out there.
I've since moved away from my Chromecast because I built just that: I built a small device, based on the pi, that interfaces between my network and HDMI-CEC. I used the DDK to add it as a device into Roomie along with functions to turn my TV on, off and switch between inputs. Like a lot of people, I have an IP enabled TV, but cannot use IP to turn it on, so that was the function I needed most. I also found that after switching the TV on, the IP control seems to take a minute or two to become available, so it is much more convenient to set the input for an activity via HDMI-CEC versus IP control to my TV.
The best part is, now that I basically have a network-enabled device which allows me to send raw CEC commands, there is no limit to what I can control via CEC by simply adding new commands to my device via the DDK.