What is the child before landing? In limbo?
No, the child is the same citizenship as the mother, or a citizen of whatever country the airliner is from, depending on that nation's laws. If it were an American aircraft, it might be considered an American citizen, even if it occurred in another country's air space. Landing would change nothing.
What is the threshold for acquiring jus soli? If it's not being born inside the boundary, and it's not touching the soil, by what method does it operate? Again, I am reminded of the Liberal argument for "Instant Personhood" once a child emerges from the womb, but "non personhood" just prior to that time.
Of course the pro-life and jus sanguinius concepts are in complete agreement with each other. (From the moment of conception.) This sudden and wrenching change from one status to another seems to be a sort of ad hoc.