...rapidly reducing viral loads to undetectable levels would seem to be what you would want in such a trial.
True—provided that the virus doesn't quickly become resistant to the drug.
I'm not saying ReViral's RSV fusion inhibitor won't work well, but rather that its MoA leaves a smaller margin for error than an N-protein inhibitor such as ENTA's, and it's more likely (IMO) that it would need to used in a combination regimen.
There may also be differences in safety/tolerability to distinguish the various RSV drugs in development.