Nice to see the proceed of you plugin! Only a small idea, but maybe are you interested.
First would be interesting if GA is possible to response numeric values of a gBrigde devices. If so this could be used for announcing state of variable devices for example. I tried it with a dimmer devices I am added to gBridge. Maybe I asked in the wrong way, but I only got the answer that the device is on or off. I found no way to get the dim level. But maybe this could be achieved somehow.
You shortly added the thermostat device. Is it possible to let GA anounce the current temp? I have no thermostat device, but many aqara room sensors which provides temp and humidity.
My idea is to use your aux function. The numeric return value of an api call or script could be for example the temp value of a aqara device. This value should be extented by an unit °C/% (choosed from a pre defined list or free text) within the sub device config. Voila I can ask GA for the temp of the living room!