@pstuart is a grandmaster at integrations, but I think he’s only been working with Control4 sensors, a much simpler task than a device like the extender. But he would certainly know more about what might be hack able.
As far as out of the box integrations, though, ZHA 1.2.
He has been able to make some ST devices controllable by Control4, but that still requires a Control4 license.
