The scenario I set out was a player goes air born to catch the ball, and who, without being touched, loses the ball immediately upon hitting the ground, and the opposing team recovers the ball. Accordingly, there are no 3 steps, there is no TD because the goal line hasn't been crossed, and since the player hasn't been touched, the ball actually would be a fumble under the rule you propose. For that matter, even if he took the 3 steps and then went to the ground without being touched and lost the ball it would be a fumble. The "ground can't cause a fumble" rule only applies when the player is contacted by the defense, because then it would be a dead ball when he hit the ground. If he isn't touched, the play isn't dead, therefore losing the ball when he hit the ground would be a fumble that either team could recover.