Not a structural engineering expert, but beyond a certain depth for tunnels (depending on soil type I believe) there isn't a structural risk to buildings above,

Not a structural engineering expert, but beyond a certain depth for tunnels (depending on soil type I believe) there isn't a structural risk to buildings above, especially at the tunnel diameter sizes suggested by Boring co. With airspace you have several problems - noise, collisions, crashing on whatever is below. Having said that, I think we'd all love a safe, electric VTOL vehicle. I don't think they would be allowed in densely populated areas though, same as drones above a certain weight.