I have never read the protocol spec (as I wouldn't understand it anyway) so I'm not sure what it told you. As far as replicating the function of the Stargate on another platform, I would be open to that but have never found an easy way to do it. Some of the issues include:
I use lots of voice announcements tied to events. Most of them involve speaking the value of variables (thermostat setpoint, outside temperature, total runtime of the furnace, etc.) Speaking variable values is not supported on a platform like HAI or Elk M1 so I would have to run a PC platform like CQC.
I also have a lot of events trigger when a variable changes value (if setpoint changes value then speak new setpoint); also not directly supported by HAI or ELK.
I have about 80 hard wired digital inputs which most PC based systems can't directly support so some kind of control panel is still required to support that. (Both Elk and HAI can handle this but don't offer any compelling advantage over stargate in this area).
The internal voice board on the stargate has robust internal switching for interconnecting line-in, line-out, phone-line, and speaker connections. This could probably be replicated with a combination of a sound card, modem, and some external equipment to manage the switching, but it wouldn't be pretty.
I use lots of RS-485 devices. Besides the 8 thermostats I have a device to display messages on a TV screen, a bunch of LCD text keypads, and some LED keypads. These are plug and Play with Stargate and would probably be a lot of work to implement under CQC.
The web interface is also plug and play on Stargate but I assume that is also true for CQC?
I have figured out how to interface my Stargate to Slimserver and Virtual Weather Station. It isn't clear how I would integrate these two critical items with CQC or ELK or HAI or whatever so I am still holding back until I can see a specific migration path.