It is - a lot of projectiles explode above ground. Two examples are the UEF and Seraphim t1 mobile artillery, that 'explode' above ground to create child projectiles. We can do the same for strategic missiles, but then without creating the child projectiles .
However, the effects are made with the idea that the missile impacts on the ground. Those will look off when we do this. And hence, until someone spends a few afternoons adjusting those effects, this won't happen.