I've not seen that thread. There are a bunch of us with a combination of Honeywell HGI80/HGS80s and/or home-grown radio hardware who are listening to the Evohome radio traffic and decoding it for display (typically in Domoticz).
Evohome doesn't require an internet connection (which, IMHO, is one of its strong points). The system will function perfectly well without one. It will keep following your schedule, etc. In fact, it doesn't even require a home network of any kind.
That said, you can in theory put all these bits together. The various hardware bits have the means to transmit Evohome messages and, at the moment at least, the Evohome controller will happily act on those. This would allow you to have your own control of, say, set points and schedules, etc. How well this would interact with the controller making its own set point changes is another question. It wouldn't let you do anything like having more than 12 zones though because that's a limitation in the controller.
However, if you wanted to cut out the controller completely, that would be a different matter. It's possible in theory, but I think it's actually a very tricky algorithm to get right given all the variables. Plus, I'm not sure the community as a whole has deciphered quite enough of the radio protocol to fully implement this yet.