> you need a specialized bunker buster munition to penetrate them
Which already exists. For example, India (so that you cannot say "this is something only available to USA) has the Agni-V (https://en.wikipedia.org/wiki/Agni-V) that supports a 7.5 ton bunker buster with Mach 24 terminal velocity. It costs $5 million each (like a battle tank).
Your squishy 747 moving at Mach 1 is nothing in comparison.
What other countries do already have something similar, or will have something similar, let's say, in the next 5 years?