But I'm not sure American broadcasters could adjust to a game with only two halfs of 40min each, no stopping of the clock and nowhere to stuff their abundance of ads.
I wouldn't mock the Americans too much for their famous love of advertising. I haven't found a sport yet that is as much a slave to advertising as Aussie Rules. Try to find a square meter of space[1] at an AFL game without advertising - even the ball itself is adorned with the golden arches.
[1] Okay, some of the grass doesn't have advertising on it.....
The huge and essential difference is that in gridiron the players in the 'scrum' start ~2m appart and run towards each other head first at full speed. And while most players in rugby can go several plays without taking a hit, linemen take a significant hit basically every single play.
However, much as we aussies like to mock gridiron for the pads it requires, without the pads, players used to die relatively routinely. Take the pads away from gridiron and it would need to change and loosen up enough that it basically becomes rugby.