I would go with one of the ones I mentioned and get control of the thermostats into the Elk - then anything that can control the Elk can in turn control the thermostat...
My M1 *is* my central automation controller... for example, because my M1 does garage doors, irrigation, lighting, hvac, and security... all I had to do was buy a $50 copy of eKeypad and now I had iPhone control of all these functions in one concise place. At home a copy of Elve controlling the M1 gets me instant control of all those same functions. If I buy an android phone or tablet, a copy of ElkDroid will again get me access to everything - it's kinda nice that way - I let it be the central controller; and just use an auxillary PC for the fluffy rules that I can live without when the HA computer is off.