It's really the other way around. Major browsers have decided to phase out 3rd party cookies (with some pressure from outside forces), so now advertisers are scrambling to find alternatives. Whether or not FLoC catches on is related to whether or not it's a good alternative -- there are others out there. It's not driving the demise of 3rd party cookies, but if 3rd party cookies become useless for targeted ads, then FLoC is one of the contenders to fill the space.