There's no real evidence from what I could find that this virus mutates like the flu virus so that a treatment that works with one variant won't work with another. They all have spikes and that is partof what INO's vaccine is replicating and alerting the immune system to attack.As long as a cell produces spike fragments the immune system will be alerted.
I think Fauci like every MD I have ever met is covering his bets. MDs are not going to give a definitive answer, nor should they, when they are not in command of all the facts. He may know more than most but he is not omniscient. Moreover he has been dealing with Big Pharma for a very long time and understands that if he favors one vaccine over the other they turn on him. Its a cutthroat business normally and billions of dollars floating around for a successful vaccine sharpens knives even more.
Getting a conditional grant means you have to produce and no money until then. I suspect that if one of the BPs fails in its vaccine search they will look to buy the likes of an INO.