Except, I still don't think there is a test that works sufficiently in the pre-symptomatic stage.

A reliable test, probably tests, at the airport would help weed out as many potential passengers infected with Covid-19 as possible (and thus be a huge huge factor in reducing transmission risk on the plane and in the airport).
However, other mitigation factors need to be layered to further reduce transmission from people not able do be detected as being infected and shedding.
This is where masks come in; where persistent and resolute cleaning and re-cleaning of high traffic surfaces comes in; and, where regular personal hygiene en route comes in (and the ability to safely do that).

It seems to me there are ways to make this all work; but different airports, airlines, governments will have different views and the minimum mitigations needed (in my view) involve 3 or 4 layers not a magic bullet.