If the variable for the Blinker data payload is added to gv.py, then I would not have to do anything. The user could configure the MQTT message payload to include this information. It would probably be a good idea though to include this variable in the default configurations supplied.
I have posted on another topic a problem I encountered with the weather_level_adj plugin. This plugin encountered a serious error which it could not resolve, and printed a message (which in normal operation I would not see), then repeated this constantly. It seems that this could be another use for MQTT – to enable a plugin to get an error (or success?) message out to where it can be seen?