You have to judge at what point does he have control and does he have control long enough to have had the time to make an act common to the game. Those saying TD are saying that he gained control with 1 foot down and then he put the second foot down and reached across the goalline. Taking that second step and reaching are both acts common to the game. If that's what you are seeing, then the process has been completed. That's a whole lot to process at live speed. At live speed I would have incomplete and in my opinion live speed should be how you make a ruling.