I think at its core it would just be about helping train the Sense to detect specific events.
The simplest of integrations would be that the Nest can tell the Sense “hey, I’m turning on the 2nd floor heat now” or " only the fan is running, I turned off the compressor". Since the Nest knows what it is doing, it can pass that info on to Sense to help them build / detect the device. The Nest knows the name of the zone, the type of HVAC (heat/cool), what kind of heat (radiant/electric/forced air) and the fuel source, that is all info that Sense can use to help detect the power signatures faster.
I’m sure there are other integration possibilities as well, but that is what I am seeing as the base integration at this moment.