Partial payments like that are an investment in the chance that Boom will deliver something exceptional; they avoid not being in the first wave if Boom succeeds.
It doesn't mean they think the chances of Boom producing a worthwhile product are > 50%.
This doesn't make sense to me. The airline should have a netter idea of what passengers can and cant afford. Is they are confident enough to order planes, I feel its safe to assume the demand is there.
More importantly I'd like to know what the cost and payment down is. If its $100k you might have many taking a high risk punt. If its $20m you've got some real commitment and confidence.
Business travelers will be buying these. They'll have a travel budget, the trip will be justified, and the company card will pay. It will pass through silently and might eventually show up in a travel policy that states how only executives are allowed to book supersonic flights.
Not only won't the passengers be mad, they might even be more likely to fly given the reduced travel time. It will now be much faster from NYC to London than to the Bay.