No, because the second someone picks off the pass, he's kneeling down, because the game's over. Sure, if the pick is deep over the middle. But considering how often pick 6's come off passes in the flat where there is nothing but clear sailing for the defender, you have to think most guys are staying upright and running it in to clinch the game. A safety coming off a possession that starts with a kickoff, instead of a punt deep inside the 5, turnover on downs following a goal line stand or red zone turnover, is highly unlikely. Yeah, has anyone even seen a safety occur after a kickoff?