The light at the end of the tunnel will come when the prevalence of the virus decreases, whether it's by everyone getting it and recovering/dying, and/or efficacious vaccines. An app does not solve the underlying problem.
The problem is that almost all experts have agreed that this virus isn't going away next year, or even the year after that. A vaccine will help, but because of people refusing to take it, we probably won't be "safe" until well into 2022.
We've seen clear evidence that airlines cannot wait that long. They will go under insofar as not being able to recover. Something needs to....has to happen before then that will allow some level of transcontinental travel.