I have a wet blanket:
Even if "everyone" "really" "is" poly, it's not as though everyone is going to be compatible, so I see the OP as an exercise in intellectual masturbation (not in a bad way, unless you'd consider masturbation a "bad" thing). Even if it could be proved 1000% beyond a doubt, I don't think it would make too much difference in practice:
"ok, so everyone is polyamorous to some degree whether they realize it or not. What now?"
Do we all go out and get fluid-bonded with each other?